I use both Festool and Milwaukee.  My tools ride in all three forms of systainers but most of my screw and small specialized tooling live in Milwaukee low profile packouts with interior bins.  I had bought the Milwaukee cart with attached bin but sold it so move to the new handcart that the packouts attach and have two of the two drawer units. 

I have loads of packout and use the drawers. Just like @rst I got the cart, but find it useless. The handcart with drawers is really the smart option. I could go on and on about what I'd like them to build. At the top of my list is a folding cart that will collapse and then lock into a packout and not take up more space than the a large packout. I want the cart to be modular so I don't have to find a place for it. Stack it, please.

I dislike my systainers and may move everything to packout. I dislike them for the same reasons as most others that dislike them.

Lots of 3d printed packout adapters and useful things available. I've mounted feet on coolers and other boxes so they can lock in.

The drawers are great. I use them every day.

The best adaptors that I've seen have been custom plywood made by users.