Is the Mio durable?

Prior to posting questions on specific toys, you may want to read a review or two, which may answer your question a lot faster. On the main page of this toy, I found this quote on how long you should wear it for, so even if it lasts for a longer session, you shouldn't wear it for one:

"(Cock rings should not be worn for longer than 30 minutes at a time with an hour between sessions)"

Also, it is made of silicone, which is one of the best materials money can buy in the toy world

Hope that helps!

Silicone can last a very long time. It is a great material.

is it water proof?

It looks very well built and silicone does last a long time. It is waterproof.