Rustpot
M Frame Lover
Take it off (pull the rubber off the frame) and then see how well they work.Also, I feel like it's kinda overrated. My flak jackets aren't all that grippy, and are pretty slippery when wet, especially after I get sweat and oils on it.
Clean rubber will grip better than dirty.
And it might be the Flak Jacket is too wide for you and doesn't have the appropriate stem tension to grip with.