Here's another alternative -- an old Kodak Retina frame finder. Aluminum, VERY well-made. Adjustable for infinity to close-up. Works fine with my 16-45 lens... but not with long 200mm telephoto... the farther you get away from about 50mm (75mm equiv), the worse it gets (like all of these viewfinders).
Bought from Keh, as 'Kodak Retina - Prisms and Viewfinders ... FRAME FINDER C W/LTHR CASE; W/IB F/IIIC/I' ... see
Kodak Retina FRAME FINDER C W/LTHR CASE; W/IB F/IIIC/I - KEH.com
Best of all -- that Kodak red dot! Eat your heart out, Leica!