I purchased my home in February 2009 and it came with a water filtration system from Arizona Environmental Progress so I can't speak to their sales tactics. I did have a costly resin replacement for around $400 after I had to refill part of my pool. In hindsight, I should have switched off the water filter system. I also had to pay $200 for a valve rebuild the same year. Since then, the yearly service for filter changes has run around $170. The water in our home is really soft. When we go on vacation and rent houses or stay in hotels, our hair immediately feels the difference. If we leave water in a cup, it just evaporates and doesn't leave any residue behind. There is a reverse osmosis system underneath my sink as well. The water from our spout gives us filtered water taste all the time. There aren't any hard water marks or sediment build up in any of our showers. Most of the build up in the showers is from soap/shampoo splash.
I guess we're a little spoiled now because I can distinctly taste at restaurants whether the water they serve is filtered or not. Sometimes we joke that some restaurants serve tap water so that you'll want to order a drink (not from a soda gun which uses the same tap water) from them.
Apparently, the previous owners bought a system that is used more in commercial applications, but our system works fine for us. We always get a free bag of salt every time they come out for service. Several of the technicians also showed me how to dilute the Hydro-Rinse so that it lasts longer. Keep in mind, this system won't make all of the water in your house taste great as it flows through various pipes so we only drink the water from the reverse osmosis spout. If the service was cheaper, it would be even better. However, I think given the reliability of the system after the resin replacement and valve rebuild maybe it would require more maintenance calls.