I have the small one on a heavy stocked 250+ TWV system and it rocks. I will say one thing, they are under rated ffor what they can handle.
And Dave will down right hook you up for customer service aand "mods" to a point. I have the small one and have the medium cup on it. I even have the medium pump i can put on it. These things are built like a tank with really thick acrilic and reallly easy to clean.
Top notch and underrated.
I have used the small one on a 180 gallon fowlr with a beyond heavy bioload and it worked flawlessly.
Also used a custom commercial series on a 1400 gallon reef and its rock solid.