I have one and it is great! I just cleaned it last night and boy that stuff was stinky. I have not done any modifications to it at all. I really have nothing, but nice things to say. I bought mine on ebay because the dealers there are WAY cheaper then any other place. For the price I really don't think they can be beat. The one I purchased is a knock off of a small deltec.
The only down side is the instructions are almost non-existent and the output tube is "universal". I had to cut my tube shorter.
I am actually seriously considering buying an octopus calcium reactor.