Hi all, I pre-ordered the adapter and just got it in today. I am planning to do a thorough review of it soon, but for now I've just been messing around with it. As far as I can tell, there is no loss in sharpness or light blooming or any of the other weird effects that adapters with built optics often have. I'm not sure if it makes lens necessarily better, but I don't think it makes them any worse. It really is like having a full frame camera.
The speed boost really works too. It feels kind of subtle from F1.4 to F2 but it's really obvious at F4 and slower.
There is one caveat and it's potentially major and that it doesn't seem to focus quite to infinity. It's almost there but it's just a little soft. I think focusing in general is thrown off a bit as compared to the focus marks on the lens. Like, it might focus a little closer than normal. However, I could be wrong and it might focus to infinity. I haven't done the proper tests to confirm this.
All in all, this looks like the real deal. And it's really not that heavy to address that one dude who was saying something about it being 197 grams or whatever it weighs.