I originally ordered my RO system from an un-named internet auction site.. The filter was ok but not great. After learning about thefilterguys I have to agree with Boomer and add my own. They were able to outfit my system with all of their filters/membrane aid me in fine tuning my system for my own water needs and I now have 0 tds coming out of my RO/DI system. Even though their paypal won't let you "cross ship" to a non-authorized address they went the extra mile and shipped it to my work address several times since I'm not home to meet trucks and it is much easier for me to ship to work.
Overall I give them an A+ for their help, their knowledge, and their customer service. On one order they even refunded the difference in shipping because their system overcalculated the costs. Now I live in the next state over from them, and in reality am only about 4 hours a way by car.. But its this extra efforts on their behalf to ensure that I have a high quality system, their going the extra mile (for 5 bucks) makes me a customer for life.
I can't say enough good stuff about these guys.