I have used this filter for both marine and freshwater nano tanks. It comes in various sizes but I am not recommending the larger sizes. If you are needed something for a bigger tank (50 gallons or more) then I recommend going with a proper Fluval canister if you are looking for a canister.
I used the small (10 gallon) version of this. It provides excellent filtration which includes a media chamber and like all canisters you just get two tubes going into the tank, rather than something that sits across the entire rim. This might not seem important, but often hang on filters can get in the way of rockwork, plants or other aesthetic features. For example, I am setting up a paludarium that has wood on the rim itself. A hang on filter just won’t work. In that case you can use one of these (or an air-driven sponge).
The only negative I faced was that the hoses, when new, are stiff. I found that by bending them and pulling some on them they softened up and I was able to lay them how I wanted. I still own this filter so that is saying something I think. You can also modify it to your needs. I actually took out all the insides and put a few small pieces of live rock when I was using it on a marine tank.