Good evening (UK time) @masonwoodshop  - So here's my story;

I'm a professional woodworker. For many years throughout what now seems like ancient history, I used a Nilfisk 26/21 as a dust extractor. Great machine, super-reliable, great customer support, cheap and readily available parts such as motor brushes, a 25-litre capacity, power tool takeoff socket, and stupid-cheap aftermarket bags from eBay. Then - I took on a commission to build 8 x vast oak doors for a large old building, which involved a colossal amount of shop-based machining - way more than I'd ever had to do before. I was filling three or four bags a day.

Ouch.

So I bought the then-newly-introduced CT-VA-20 because I'd seen a video on YouTube and thought that it looked like a great money-saving gadget. It was of course - capturing almost everything which my routers, sanders, planer, jointer and other tools were producing - but I had this thing sitting on the floor next to the Nilfisk. Very cumbersome, very awkward, very impractical. It was at that point that I realised that it wasn't designed to be used with any old vacuum - it was designed to be used with a Festool extractor (which I'd always thought were crazy-expensive at around 3x the price of my Nilfisk, and had consequently always dismissed from my wishlist). So I drank a nice bottle of Rioja just to sharpen my mind, and - inevitably - placed a late-night order for a CT26.

Tip of the day - if you're unsure about whether to buy a new tool, drink a bottle of something nice. As you drain your final glass, you'll realise just what a great idea you had, how low your current credit card balance is, and how much this new tool will improve your life. As a 3-decades-plus pro, I've always taken the view that the purchase of a top-quality tool only hurts the once - on the day that you pay for it. The purchase of low-quality tool hurts every time you use it.

So anyway - the game changed from that point, and I generously donated the Nilfisk to my daughter for her house (she loves it just as much as I did, and I showed her yet again what a wonderful father I am). The cyclone sat T-Loc'd on top of the CT26, and effectively became an integral part of it. And now - I honestly couldn't imagine life without it. Since then, I can recall dozens of jobs which have involved emptying the bin multiple times a day, and every time I do that, I'm thinking "that would have been another ten-dollar Selfclean bag".

The most surprising aspect of it for me has been that Festool only claim that it captures heavier particles such as planings, sawdust or router debris. But it doesn't - it captures way more than that. I'm currently working on a kitchen job where there are large, heavily stained sandstone arches at one end of the room - so I had the sandblasters in, who did a great job, but left the entire kitchen an inch deep in blasting dust and sandstone. The amount of that dust which ended up in the cyclone's bin (and the associated lack of material in the CT26 bag) astounded me.

Downsides? Only one - it reduces the suction. Some very clever guys on this forum have done a variety of tests on this to calculate the actual % drop in airflow - but under everyday, real-world conditions, it doesn't make any difference. The only thing I do is that if I have a big cleanup to do at the end of a job, I'll use a regular soft sweeping brush to move sawdust into a pile, suck it up using the whole rig, then disconnect the cyclone and do the final vac-up using the CT26 'direct' so to speak.

I like it. A lot. I'm not a Festool expert so I don't know if it will T-Loc to the top of your extractor - but I know that other knowledgeable members will be along any time soon. And regarding your point about it supposedly only being compatible with the larger CT extractors - there's a video on YouTube in which our forum resident Peter Parfitt rigged up a CT-VA-20 to the little Systainer-sized CT-SYS. It worked.

I hope my little ramble helps.

Kevin

@Kevin, I did not partake of any tall glass until I settled for the Dust Deputy. But it works just as well as the cyclone. I went from replacing the bag every two days (A slight exaguration) to weeks to empty the drum. I not only saved the bag, but i had more time to satisfy my thirst.
Tinker

Liquid-based decision making started me down the Festool path and I don't see why that shouldn't change my decision making process now.

My profound respect to you, sir - spoken like a true FOG disciple. I hope that whichever route you take hits the spot for you. Greetings from a saturated, flooded-out England 

Kevin

I will try to chip in with a bit different perspective.

TLDR: If you need to ask, the you should get the CT-VA and forget the DD.


The long:
-------------------
The DD and the CT-VA are actually different tools in their use cases.

The CT-VA is optimized for low-air-volume tasks while it *can* do middle-volume tasks. It restricts the airflow because that is the only way a cyclone can achieve reasonably good efficiency at low air volumes. A cyclone relies on air speed to do its work, and at low air volume - like when using a sander - the only way to achieve sufficient air speed is to make the cyclone internal "nozzle" low diameter. This in turn affects the high-volume tasks.

The DD, on the other hand, is optimized for high-air-volume tasks like planing, tracksaw use, Kapex use etc. The price to pay is that with sanding the efficiency of DD will be mediocre - the wide channels will not see sufficient air speed for the air cyclone to do its job.

This makes the CT-VA the more "universal" tool, as you can always remove it from the loop if the air volume is too low for your liking. You can however never get good efficiency for a sanding job from the DD.

I’m with Chuck and my DD performs stronger than my CT-VA but conforms to the “system” for on site

In my original post, I said that the CT-VA reduces suction - but in every day, real-world action it doesn’t make any difference. Take it from someone who uses a CT-VA between 2 and 6 hours a day x 6 days a week - it doesn’t. I personally feel that starting to throw around scientific airflow rates and percentage drops is overcomplicating things and probably unhelpful to a guy trying to make a decision.

Here’s my 2 cents FWIW.
I own two DD one with a shop made box with a footprint of a systainer and the other is a UDD
I like them both. They seem to do what’s needs to be done. These have been in service long before Festool came out with their CT-VA20.
If I needed a new one I would probably give festools a try since it seems a little more compact.

After reading all these spec about different volumes of air moving though the two different cyclones, it would be interesting to see a test with the Oneida in front of a Festool cyclone.
I’m more of a visual guy and the facts collected in the bin.
Rick.

Thank you for your replies. All of them are quite informative. We do have some real experts, both technical and experienced, on here regarding dust collection.
Oneida has a good reputation with their Dust Deputy. Of Oneida's products I have considered the Ultimate Dust Deputy due primarily to static concerns. The negatives are that it appears quite tall and maybe a little unwieldy for rolling it around the shop, and I wish you could see the bin capacity.
The CT-VA solves those concerns and I am thinking now that the comments about suction loss I've seen on the web may be a little overstated.

Thanks for the info.

This thread has been far more informative than I anticipated and I'm glad I posted it! Right now I'm about 80% sure I'll the CT Cyclone route, with the other 20% being for a DIY Dust Deputy - now I just need to convince my wife that $579 CAD is an investment in my health and not ego to have more green in the shop!

For a normal 'craftsman/woodworker' I doubt you will tell the difference*  between the CT-VA and either DD except in the ergonomics. The DD is pretty unwieldy compared to an integrated unit on top of the vac that packs nicely.

If you are a regular woodworker or contractor the CT-VA will serve you just the same except it will be nicer to use

*extremes where I noticed the DD gains an advantage
- suction advantage if vacuuming using two lengths of D36 hose or longer. Or any other flow restrictions like elbows or adapters.
- extremely messy jobs. Getting it in places you would not want your festool in. Vacuuming dirt, liquids or rocks : Because you just don't care and it works fine and it's easy to wash and the buckets are easy to clean and replace

The DD2.5 gains an advantage over the DD for sure. My vacuum also runs quieter since there is less restrictions and I can run extremely long hoses again. However it's even worse to pull around. I have not built any contraption I see many have. This would solve an issue of pulling around but it would not be compact at all.

https://www.amazon.com/vdp/0f423b5e5f334ad1a91b2d02abdd14d3?product=B09W68X4HJ&ref=cm_sw_wa_r_ib_mb_GdMw8XrziUW2C

The video suggests that one of my old DDs may benefit from an upgrade. All my DDs are used in a stationary mode.

As soon as Lee Valley carries the anti-static DD 2.5 product, I'll get one to try. It's just $54 at Amazon.

About two years ago I was in the market for a CT-VA-20. A woodworking friend of mine had one and the UDD, both working with a Festool vac. He was unhappy with the CT-VA-20 as it lacked the suction and dust collection of the UDD (and this would have been pre-2.5?).

I subsequently purchased the UDD, and have been very happy with its performance. Of course the CT-VA-20 does look sexier



Regards from Perth

Derek

Another video on the 2.5: