There can be such a thing as nickel poisoning, like it is said in Ehow. If you are going to be wearing those ring frequently for long periods of time like you appear to do, I would think seriously about getting a good material upgrade.

You can also consider stainless steel: Titan Mirror and Titan Brushed, but they looks quite similar to the size of the Alchemy.

There is also the more expansive silver sterling cock rings like Silver Celtic Cock Ring, but it may be a little too small and wide for you. I did not see any other one in silver on the site, except one that was too small and not in stock.

And also this product made of semi-precious stone, which looks thinner than the Alchemy band. It comes in sizes that should interest you. And in pretty colors, unless you insist on using a metal: Green Aventurine or Black Agate
I know it's more expensive, but it beats buying another set regularly.

Hope it helps you somehow less