I don't know. I'm not a huge fan of them. I tried it once, and it just didn't really do it for me. I'm sure it could be fun during sex, but then again... I don't really need it.
I would think that during an erection, cockrings are not that healthy because they restrict blood flow too much (in my opinion) during an erection and make the blood vessels in your penis very rigid. If you like wearing it merely as an accessory, don't wear it too tight. That's about all I can help you with!