I've tried cock rings before but had always given them up quickly just because they felt uncomfortable at times, and I also hated taking them off after just 20 - 30 minutes (not easy to do when you wear them around your balls and are still hard).
I tried the J'Naja with some trepidation, but am thrilled with the results. I can wear it comfortably for the whole day, getting a nice, steady dose of stimulation (the perineum massage is especially wonderful). The molded material doesn't dig in. Aside from that, I'm more sensitive, my erections are fuller and longer-lasting, and my bulge looks bigger.
One piece of advice -- if you're between sizes, as I was, go with the smaller one. I like the snug fit.
Get your JNaja at The Pleasure Chest