Just got the U420XW for Christmas and been on a couple of trips with it (7 day international and long weekend domestic). I'm a big guy (6'+) but a light packer so I only carry a laptop bag (that I can stuff an extra shirt/socks/underwear into just in case). Note that I've not done much travel and have used a couple Kirkwood signature rollers, and odd collections of gym/duffle bags so I don't have that much experience here.

some overhead bin fit notes:
UA 747 new config C: didn't fit wheels in, had to go sideways.
LT A340 C: Wheels in just fine.
757 Y: Wheels in just fine

Tried wheeling down the 757 E isle and it was extremely tight.

The suiter's a bit anoying as you can't take the whole thing out if you don't need it; just the last third. Also as others have said it needs a bit of space to load (~5') since you can't take it out.

While I like the concept of the flat bottom, but I think I'd rather have integrated handle and lift up plastic board for a little more space. Note that when put the bag down the back pushes gently into the bag space. Again I'm not a frequent traveler so I don't have a lot of experience with other wheelers.

One nice feature is the "legs" are on the outside of the expansion zipper so you won't be dragging the bottom when overpacked and expanded.