I had terrible luck with one, it didn't fit well in my 12 gallon nano cube and didn't seem to be doing much, so I eventually just gave up and removed it. I hope it works out better for you.
I have one and it is doing decent. But as the previous posts say the top of it (with the filter) likes to slide up and almost off. It also creates a huge bubble problem. And sometimes spits water out of the top instead of a slow stream out of the top.
Anyhow I don't recommend it but I have one. Can't afford spending $200 on a larger one yet. I spent my money on a MH light.