I would think they would be uncomfortable too. I wore a halloween costume a few years ago with a corset top that sucked me in really nicely, but it was just so stiff and weird to move in! I guess it's also like a bridesmaid dress I wore with boning in it... when I took it off at night I had deep marks in my skin after peeling it off
I would think Spanx would be more comfortable. I have a couple of friends who have Spanx and swear by them! I am usually all for beauty over pain (as my massive collection of 4+ inch heels will show), but when it's uncomfortable around my stomach and ribs, it really bothers me.