I have an AquaC EV 180. I've had it for about a year now. They do work pretty well. I have it on a 180g FOWLR and I feed heavily. The air intake elbow gets clogged pretty regularly with salt creep. I have mine in sump and would not recommend putting it hang-on, but in-line would be fine too. HTH
Thanks Jenny. If I used it, it would be externally. I downloaded the instructions on it and a few others and th AquaC seems pretty good and manageable.