I will be building a new workbench before too long, and figuring on putting MFT tops on it.   It would be 8' long and basically look like image below, just to match the look of my other workbenches.  I would be using the Festool tops rather than making my own.  The area below the top would be storage.   My other workbenches have drawers, but I am not sure that is the best idea for an MFT type workbench.   I might put hinges doors on this one for better bottom access.  Can I please have some opinions:

1) Should I have good bottom access to the underside of the MFT tops ?   

2) Dust build up.   You think it would be a good idea to put a sheet (possibly removable) to protect dust falling through the holes ?

3) I am playing with the idea of putting a flip-down rail in the center, for cross cutting.   but I already have a fair sized table saw with a good miter guide.   For those with both, do you commonly go to the table saw or the flip down rail ?

I think it's always a good idea to have easy access to the underside.  I know there are some people who use things like the festool clamping elements without locking them down with a knob underneath, but if you ever wanted to incorporate something like the kreg automaxx clamps mounted on a bench dog base (which are really useful for workholding when dominoing boards), those can only be used while locked down.

As to the rail vs table saw question, the real advantage of the MFT when cross-cutting is the batched cut capability with the flag stops off the fence.  For one offs it's not necessarily more efficient than other methods (provided the board is not too big for something like the table saw miter gauge).  So if you were able to incorporate a fence system or some other method of making repeat cuts, then I feel like it would be a useful to add the rail.   

As for the dust collection question, I think it's about your tolerance for mess more than anything.  The underside of my bench, which is 1.5" maple but with MFT hole pattern, does get funky over time from falling dust, but I don't really mind as long as I vacuum it up every few days.

Maybe you are familiar working with MFT tops but I wasn't when I made three fancy MFT slabs for a 4'x8' workspace. I purchased several bench dogs to start utilizing the MFT. At the same time I discovered the TSO square and parallel guides and have never used the MFT tops for their original intention. I do find them very handy for clamping and assembly. You may want to look into making your own tops with less holes and maybe clamping slots.

I am basically in the same position as you were Mike.   I have never lived with an MFT table, so not sure what to expect and what will be most useful to me.   But I just finished another bench, with a small number of 20mm holes on/around my front-vise, and already finding them handy as stops.

From the feedback received here, I think I would put in a removable dust sheet under the surface.   And put drawers on the bench rather than hinged doors.   The bottom of the MFT sheet would still be accessible, just that I would need to remove the dust sheet and at least open the drawer, possibly remove the drawer.   

I will hold off on the flip down rail for now.   I have the HK 55 EQ with the 420mm rail, but no other rails right now.    Possibly get a longer rail, and get some experience using it manually before deciding if its beneficial to make it flip down.

Also, if you are new to MFT tables I have learned from others to use a waste board under your workpiece so as not to score the table. I use cheap 1/4" (ha-3/32") ply.

After retiring, I gave up my dedicated shop and now work in my garage, so portability was important. I really liked the MFT concept, so I purchased a couple Festool MFT tops and set them up on my sawhorses.  It's incredibly stable and gives me the work area of a full 8 ft.  I have built rolling cabinets for all my Festool tools, so depending what task I'm working on I can roll the cabinet under the work top for convenience. I like having the flip-up guide rail at times, so I made a bracket to hold the guide rail bracket I use.  If using the MFT top, I would recommend keeping 3" to 4" of space under it for access.  Also, if building a bench, I recommend drawers vs. doors also. Finally, I've never had a real problem with dust.  I use the Festool vac hooked to most my dust creating tools and then just vacuum and blow the garage out when I'm done.  Works good for me ... good luck with your decision.

To pile on Glenn's post. I work out of my garage. I have three 32"x48" MFT slabs that are placed on TrackTubes & saw horses (borrowed someone's idea.). I store them on a cable lift system and can be ready to work in 5-minutes. This with TSO products has been the most efficient/accurate/fun process I have ever had and I've been into this hobby for over 30 years.

@Grev  Can you show more details on how you attached the rail hinge to the top? - thanks

I'm curious, how sturdy are the Track Tubes in the saw horses ... if you were clamping wood and hand planing or something aggressive like this would it be wobbling around where you could mess up some precision work?

I'm planning to build a 36" x 72" table over the top of my 8020 sys cart and was planning to build it out of 8020 also until I stumbled upon these track tubes today.  Eventually I want to get the Festool VAC clamps so I thought the 8020 would be good for that but perhaps some adapter can be made to mount it to the MFT top like Ron Paulk does with his portable table saw.  Anyways, the main issue I see is the sys cart is 60" so I've only 1 foot of clearance and these saw horses easily take up 2 feet.  Are there any other support systems for these people are using which would take up less space and yet remain stable?