Hi !
As I'm aging, my vision is becoming worse. I've tried several loupes, but found the current set up I now use very good and comfortable : it is made from a projector lens (an old plastic Rollei lens made in Singapore I got for a pair of bucks) mounted on an opaque plastic tube. The trick is to custom cut the plastic tube at the exactfocussing dimension of the lens. This way, you rest the "thing" onto the GG and concentrate on focussing. Added bonus, as the tube is lightproof, you do not need the dark cloth and can keep your brain chill (usefull considering the outdoor temp these days).
If you loose or break the set up, you won't break the bank to find a replacement, as it will be for a Schneider ;-)
Just my 2 c...