As I've always understood it from several GGCA members, in the US and Germany, the wrist mounted sight to be utilized is as a diopter. I believe there is still manufactured the Merit Optical device and Lyman used to make a diopter that sticks to your glasses lens with a suction cup that is much like this Merit. I just use a leather punch and punch a hole through several layers blue painters tap. I call it "The Magical Blue Painters Tape Diopter". At 72, it is a great aid to my open sight shooting...which is about all I shoot.

https://www.midwayusa.com/product/1015167397?pid=978528