I talked to the manufacturer today regarding the concentration of chlorine as the level goes down. The official answer is that the concentration remains virtually the same until there is only 0.5 gallon of chlorine left - something to do with the way chlorine and water react together. The only issue is if you have very high alkalinity and calcium, it causes excessive scaling on the floats that needs to be cleaned out. The person I talked to lives in CA and has the 8 gallon version and keeps 5-6 ppm concentration with 100 CYA level. By the way they have certification for this unit to be used in public and commercial installations and if the concentration would not have been constant, they could not get this certification. All in all, I think I will order one and give it a try.
Amir