There is a wide variety of different cock rings. When used correctly, the ring restricts blood flow to the penis, thus prolonging the "staying power," and ideally, they can also serve as a non-chemical alternative to Viagra and similar medications
Another advantage associated with wearing a cock ring is heightened sensitivity to touch and a stronger sense of pleasure – along with a corresponding visual enlargement!

Adjustable cock rings are the perfect option for men who want to try using a cock ring for the first time. Since they are adjustable, they offer the possibility to vary and control the level of constriction. They can also be worn as bracelets, allowing you to have them with you at all times.

COCK STRAP von Boneyard
BLACK RUBBER STRAP von Push Monster

In addition, you can put them on before and during erection, which is not so easy with other cock rings. There are many different models. I prefer rubber straps or silicone straps. Both are stretchy and easy to clean.

O-rings are thick rings made of silicone. They look cool, and the wearing sensation is great. However, their stretchiness is limited, and putting them on requires some practice as they are not easy to apply – it's best to put them on before getting an erection, as otherwise, the diameter might not be sufficient to slide them on.

SILICONE DONUT COCKRING von Push Monster

How do you put on an O-ring?

Putting on an O-ring takes a bit more time and practice. To begin with, slide one "ball" through the ring, then the other (slowly), and pull the ring upward, guiding the penis through the hole of the ring. To make it easier and prevent pinching, I use some lubricant. Putting on or taking off the O-ring is not possible when you have an erection.

Metal rings look cool, and their weight adds extra tension. They are not stretchable (as you would expect), so you need to know the exact diameter that fits you, and you can only put them on before getting an erection.

STAINLESS STEEL COCKRING von Mister B

It does require some practice and experience. Metal rings make me a little nervous as you cannot remove them during an erection in case of potential blood congestion. They are not suitable for beginners as there are too many problems that can arise.

As an alternative, there are two-piece metal rings that can be connected with small screws. These at least offer the possibility of removing the ring anytime. Provided you don't lose the small screw!
I would advise against using two-piece magnetic rings as they usually don't hold well during "play."