They're advertised heavily and I see lots of folks leading them around
airports on their leashes, so they must be popular.

But all I see is wheels very exposed to damage and wheels that require
the actual storage space to be smaller than otherwise so that the
carryons will be of legal size.

I can't recall a time when I've needed (or even wanted) to spin my bag
around in place.

--
St. Paul, MN