Upon looking at how this unit works I can already tell you I'm not going to be a huge fan of it but ADA uses and recommends it so...that's why I initially bought it just to answer that question. As for what I don't like... I don't like how short the intake tube is, I personally prefer a tube that nearly reaches the bottom of my substrate (although I'm thinking I may be able to attach it reversed which may work well for my 10gal tank). I also don't think I like how the canister isn't made up of individual filtration comparments because I feel like if the filter media starts warping inward that the water will start to surpass the media altogether and send it right back into the aquarium. I also worry that the connected tubing may not be secure over time and that it may eventually leak out 10 gallons of fish water onto my carpet. I'm kind of wishing Eheim also took the time to cut or add in some additional tubing so that you don't have to cut it yourself for the control valves, makes me question the whole return policy of it. I also wish this had an automatic primer on it and worry what will happen if my power ever cuts off long enough that the unit doesn't automatically restart this filter when the power returns. How well will the 3 tiny aluminum-like clips hold together this canister? Other than that... I can't really find anything else to gripe about but than again... I haven't even finished setting this unit up due to the lowsy Eheim 2211 instructions.
Also, if you have any additional pointers for me on this then feel free to drop me a comment!