A late-night "as seen on TV" item I used with great success is the "Windshield Wonder". You can still get them at Walmart for $10. I did have to heat and reshape it as it comes out of the box flat.
I am truly stunned - I thought I would be swamped with responses.
My analysis of the few replies (well below that necessary for a statistically meaningful conclusion);
Lanky pilots probably have no difficulty in reaching the furthermost/narrowest parts of the windscreen.
The rest (less vertically blessed) are extraordinarily generous with offers of free windscreen cleaning & dinner - I just have to commit me & my Sonex to a trans Pacific flight:)
As for the great unresponsive - they either live with visual impairment (dirty/foggy windscreen) or seek out a tall slim person, of willing disposition, to clean the inside of their windscreen.