the first one i got was like silicone ring about as thick as a pencil... it worked great. It was round like a donut, so it could roll up and down as needed without catching hairs (although i usually keep pretty trim). And it's safe because you could just take it off like a rubber band, and it cost only 3 bucks or something.
Usually I go over dick and balls, cause going over just the dick can be uncomfortable. I already have a condom squeezing there.
For me, cock rings hold blood in much better any time i can't quite maintain an erection, like if i've already gone a few rounds or am drunk. Plus, they can make a hard on a HARD ON. worthwhile investment if you ask me.