I had mine for about a year, You either need to suppliment your water, and that can get expensive, or have green water in your tank, another alternative that a lot of people don't care for.
Another thing, you have to have more supstrate in your tank them the Clam is wide (they prefer sand) Most clams are also intolerant of copper, ANY COPPER AT ALLm, they are never supposed to be exposed to air and pulling them out of the sand to watch them move is stressful for them.
IMO: Good to help keep dirty tanks clean, helps nitrates (I never noticed a differance), but not much for looking at.