this is not the only time I have heard this advice.

The issue, as I understand it, with the metal ones (and other hard material ones) is that they can be a real hazard. When the ring is doing its job, it restricts the blood flow out of the penis and thus the erection does not come down as quickly. The problem arises when the ring is too tight... how do you get it off? answer? You don't, and that can be a huge problem as after a certain amount of time (not sure, but have heard 1/2 hour) tissue/nerve damage can occur.

This is why the ones that snap on or are latex (and thus easily cut off if problems arise) are recommended.

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