Kevin,
I enjoy the build of the lens. I have a VC 21 finder I use with mine, but often leave it behind because when you look through the M2 viewfinder and roll your eye far left and right, "everything" you see to the extreme is close to the Zeiss 21mm. This is best done on a tripod, because what you see outside the 35mm line is close to the 28mm, its the extreme edges that come very close to the 21mm VC finder.
I also use it on my M8.2 it brings up the 28mm frame lines. It really is as sharp and built as well as any Leica lens. I just wish you were selling the 25mm version, I want to add one of those to my collection too. Good luck selling this great glass.
Lee