For me they're constricting (if they weren't, they wouldn't exactly do the job), but they don't hurt while I'm wearing them. Once in awhile, if I've been doing strenuous physical activity, I'll end up with chafing around my pits, but that's just a result of wearing what is essentially an incredibly tight muscle T.
However, five years of binding has given me bursitis in my shoulder joints, which is INCREDIBLY painful. I don't even want to know what other damage it has caused. My best advice? Get your top surgery as soon as humanly possible, or find a way not to bind for too long.