I've got a Penguin 170 on my 10g, and quite like it. IMO, one of the cons is they're not great for planted tanks (flush out much of the CO2), and sometimes the wheel will stop turning and need adjusting. There are many nice features though - they're easy to maintain (changing the cartridge couldn't be easier), self-starting after a water change/power outage, quiet, and provide very good biological filtration.