I have been running 2 400s for almost 2 years now, kinda wish I would have gone to the 500 though. My only complaint, you have to be careful when pulling the trays out the handles are pretty weak. I ditched the spray bars and just let them flow into the tank, I noticed when adding the bar it reduced the flow.
For the price of these they are a very solid filter, but like mentioned some of the parts are pretty flimsy sot as long as your careful with them they work fine!