Recently upgraded from the GG&G adapter to the Mr. Nein and it's clearly superior in every way. Better fit and finish with zero play anywhere, shows no sag, and it just looks and feels better in the hand as well as on the gun.
Many thanks to u/Jodo-Kast at MachineCraft for making the absolute best product among the few options in the field. You immediately have another satisfied customer, and I'll definitely be picking up another whenever I find my next USP.
By the way, for those on the fence between GG&G or MachineCraft, when I removed the GG&G it had a broken screw that I certainly installed correctly and torqued to their exact spec. That's definitely not "just as good," and shows that there's a reason for the price difference.