I used "Mequiar's nxt Generation car wash w/anti-static ingredient" in my Mr. Clean system this past weekend. The results were just as good and at about 25% of the cost of the Mr. Clean soap with no plugging of the spray unit.

Since the Mequiar's soap is much thicker than the Mr. Clean soap my concerns were with stopping-up the spray unit. I used 3 parts (300ml) of Mequiar's car wash with 2 parts ( 200ml) of filtered water that I got by using water from the Mr. Clean system that I caught in a 1/2 gallon plastic jug. This got the Mequirar' soap to approximately the same consistency as the Mr. Clean soap.

The Mr. Clean soap is $6 per 20 oz. and the Mequirar's soap is $7 per 64 oz. which works out to be $0.30/oz vs $0.07/oz. respectively (don't forget to multiply the Mequiar's by 0.6 since it is cut with 40% filtered water).

Now if I can just work on cleaning and recharging the filters I would be set.