Since the software edits out one of the words used to commonly designate this type of object, let me describe what we're talking about and what they do.
What this is is a tight-fitting ring of metal, plastic, rubber, leather, or cloth that fits around the base of the penis and scrotum, sort of behind the scrotum and on top of the penis, pressed against the abdomen. It can be all one piece, a solid ring, or it can be a strap or strip of flexible material that can be fastened in place with Velcro, snaps, or some other fastener.
The primary purpose of this device is to retain blood in the penis longer, so that erections are maintained longer. They are sometimes recommended or even prescribed by doctors for this reason, for men who have problems maintaining erections. Men who do not have erection problems sometimes use them to enhance the sensation or duration of their erection, too.
Most of the men I've talked to who have used them say that no, they are not generally uncomfortable. However, on the odd occasion, a solid ring (such as a heavy metal ring) could be hard to get off. Most authorities on the subject say that if this happens, the best thing to do is to refrain from panicking and just let the erection subside, which it will do just fine (just a little more slowly than normal). If the ring is made of a material that can be cut off with a pair of heavy-duty scissors, you can also cut it off if need be. Ice packs can also be helpful with shrinking swollen tissue if necessary to get one of these rings off.
However, I should note that such mishaps are rare. Most men's erections will deflate on their own given a little time to do so, even without orgasm.
Start a Revolution -- Stop Hating Your Body!