I have two of them each in a tank less than 3gal. I love them. Because they are so small, they are not made for tanks bigger than 5gal and since anything smaller than 5gal won't really maintain a cycle, you really don't have to worry about the bacteria.
I agree with Thunderloon that you will need to take apart the filter cartrage to clean it. I squeeze and swish the sponge in old tank water and use a toothbrush get the gunk out of the plastic parts. I ignore the carbon part altogether. I think I will try Thunderloon's way next time, just to try it. It sounds like it would definatly be a more thurogh cleaning.
Over all, it's quiet, fully submersible, has a spraybar attachment and is specificly made for smaller tanks.
The biggest complaint is that the five suctions cups are way too strong and it can be annoying to take out.