I have a cf-500uv and I like it, priming is a pain sometimes but besides that it keep my tank crystal clear.
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Additionally, I'm convinced the pump on it is weaker than advertised, and the plastic tubing connectors it comes with are flimsy at best.
I'm using the CF500UV right now, thought it'd be a great purchase due to price, but in the future I will ONLY buy Eheims.