Thanks for the reply. I did indeed try to explain that I was looking for this. I can imagine that the physical tolerances on the mount are extremely limited so therefore a third-party manufacturer would not be able to be compliant. (ie, too wide or too loose so there would be friction to the camera part of the mount). Guess my imagination runs too wild sometimes.
I think mech tolerance it's pretty easy for anyone able to design a somewhat decent and relatively complicate optical system; what I was not entirely trusting in the EF era was actually the lens/accessory lock, and its release switch.
Usually on lenses the releases are decently sturdy (because lenses are usually somewhat heavy), but I encountered many macro tubes, extenders, etc, with a very lousy bayonet locks; also in RF days, when I first got the R6 I couldn't find a genuine RF to EF adapter, so I got one from Meike, that was as good as the genuine in AF end electronics functionality, but the lock was yes sturdy but not UBER sturdy...so as soon as I got ahold of a Canon one, I sent the Meike back to Amazon.
So I'm very third party open, and always happy to save money, but there are some things, like adapters, where I prefer to buy original stuff, because I wouldn't entirely trust to affix for example my 1.3kg 70-200 (and my 40 Art weights almost the same, but has no tripod ring to swap lock point) to a chinese accessory, and let it dangle from my strap for hours during a wedding; another things where I never save are tripod plates, or camera straps that connect to the quarter inch thread on the bottom of the camera. Any thing that may affect stability of the camera and/or prevent the camera to detach/fall/move, is something you should never ever save on.