As can be seen in the product picture, you have to push the viewfinder further upwards in 5dmkIII, so that the whole display is beautiful on it. This makes it pretty tight with screw it and then does not sit very firmly.
The base plate can be solved only with the Allen key. Alternative Rändelschraublösung would have been great if it should go quickly and the Allen key is not found.
Pro: The base plate makes the parts the wertigsten impression and the Walimex sticker on the side can be pulled off.
Cons: Quite expensive for this Viewfinder. The tick smaller Viewfinder cost 40-50EUR times and think that's too expensive. For the price should also fit perfectly.