It is for Leica. Does not affect visibility and can still be used.
Discussion
That’s great. Which Leica do you have? I’ve got a IIIf that needs to get a CLA that I should shoot with more.
I use Mda. Leica has great lenses.
Nice I've seen some good things about the MDA. Nice to have the flexibility to use whatever viewfinder you want. I'd look at one of those turret changeable viewfinders.