To be up front..99% of them are the same, just the names are different. There are only two or 3 makers of the membranes.......Usually the saying of you get what you pay for is so true, especially in the marine life hobby, but its certainly not the case when it comes to a RODI unit. You can spend big bucks, or about a $100 and there is no difference. If anyone can tell me how their $300 to 400 dollar RODI makes better water than my $100 unit, from the infamous auction site, I sure would like to know. Just do not know how the water can be any better, when test results form those high end units comes out the same on the filters direct unit, I got on the auction site...Check out that auction site and look for a company that goes by filters direct........they have what you need, are great to dealwith and the price certainly is right.