I love them. I have 2 Emperor 280s on my 55, and 2 Emperor 400s (accompanied by 2 xp3s) on my 125. I also have a small Penquin on my 10 gallon. I haven't had any problems with any of them yet. I had several Aqua Clears break down on me.
I have an Emperor 400. I will say it has easy to clean filters. But I dont like the flow rate or the suction power when I do a water change it barely drips when water level drops 4". Comparatively I have an AC110 at the other end of the tank which I think is a better filter. It has way more flow and hardly slows at all when changing water. The AC110 is a little more time consuming to clean the media but it also removes alot more from the tank than does the 400. These are my opinions.
i have two 350Bs on my 125 and i like them but the media replacements suck if you use all four slots like i do But you can find them pretty cheap online i have found a guy on ebay that was selling like 48 replacements for 50$ after shipping that is the best price i have seen. On the other hand the AC110s have 1 foam block and Bio media ( you can also add carbon if u like) and the block is 9$ and the Bio is like 14$
have 2 emp 400 and a canaster on my 150 now, had them for a while, work great, but once i get money im gonna replace with 1 big more powerfull filter, plus after a while mine have a slight humm