Plastic Cap Wrench

This is a wrench to help open and close plastic soda bottles. I developed it for my mother-in-law who has arthritis in her thumb joints and has difficulty with unscrewing these bottle caps by hand.
I experimented with several concepts before hitting on the opposed teeth that you see here. The idea is that the teeth will flex when the wrench is pushed onto the cap. When the wrench is turned, one of the sets of three teeth will bend upward and grip the cap surface.
This particular design is a compromise between ease of pushing on (it still takes a good push) and strength of grip. If anyone makes one, I would like to know how well it works for them.