Leitax has no optics.
I understand that. The optics may be a point of consideration of one adapter over the other. The simple fact is there are other adapters out there and that's what I was trying to point out. Choice is a good thing.
Erik, I don't entirely get how putting another piece of glass in the path increases image quality. That one's a bit of a mystery. The crop factor doesn't concern me, and I'm not really sure it does many. I don't get the increase in speed either. That doesn't make a lot of sense. That one needs some explanation. That aside, R lenses are already, generally, 2.8 at the slowest so not sure an increase is really necessary. There are a few slower primes and the zooms are slower but for the most part they're 1.4, 1.8, 2 and 2.8.