Nothing really to add to what Jeff has said, supermarket brushes have made my Vykans obsolete. A brush ain't rocket science, it just agitates the dirt before you rinse it off. I use mono filament and flocked. No noticeable difference rinsing either off or on the glass. Neither will remove baked on bird muck without soaking and scrubbing. The amount of pressure you can apply to a brush head from the ground is limited, as you will have noticed when trying to push close windows.
I think too much is made of what type of brush is best. Almost any brush that reaches into the corners and frame recesses will do the job. Being in control when rinsing is more important to the end results. Splashing water over the tops of the frames is the main cause of spots and runs, not what type of brush you use. That's my experience anyway. Dai