I'm digging mine. 2 on a 275 gallon.
My biggest complaint is also their biggest selling feature - the flow pattern they create truly is a 'gyre'. It means that if you've got something annoying like internal overflows, or an oddly shaped tank, you're giving up a heck of a lot of flow efficiency.
If I had gyres from the start, I would have planned both the tank, and the aquascape differently.
Of course this means I've got a spring project
