A lot of windows are just going to be too dirty for a simple touch-free clean. The agitation and rinse from a wfp brush is the simplest, quickest, and most consistent way to get a 99% spot-free shine.
And you will go through a lot less DI resin only using it with the wfp.
If you’re really set on trying a two step process, you could get an acidic cleaner like M-37 from HydroChem. But I still think it would be simpler and faster in most situations to just use a wfp.
