I had a kinetico system once, filters were $6 from the local kinetico-selling shop in marysville, came with an o-ring, and were user-serviceable in about 40 seconds. The old filters were nasty and clogged up with rust junk after 3 months, sometimes I'd back-flush them and run them awhile longer.
Really didn't see any change in pressure or quality after changing them.
Shop may have closed up, it was on the main drag in marysville behind the dairy queen.