I have used the Carl Ziess G3 binocular loupe for about 8 years now.
I cannot speak highly enough of them, particularly when contrasted
to an optivisor.
Main advantages I have found are :-
a) optical clarity (well they are ziess lenses!)
b) comfortable and a very low weight
c) the ability to “look past” the binoculars without any adjustment
d) Focal length - the focal point is around 25 - 30 centimetres
which is advantageous when contrasted to an optivisor.
I use them constantly, in fact I put them on at the same time as my
apron and take them off at the end of the day. Magnification is more
than adequate for faceting and enamel placement.
No association, just a very satisfied user.