I have the same one as cl2ysta1 from filterdirect on eBay
I hooked mine up in October so about 4 months ago, I have 29 gallon display and 20 gallon sump. I do a 5 gallon water change every other sunday and evaporate 1 gallon a day. When I changed water yesterday I am still testing 0 TDS. For reference my tap water here in West Jordan is 225 TDS. I have been happy with it, I don't think its worthing spending more for a spectrapure unless your source is really bad.