I have Minilux with 40mm Summarit, and it is great lens, everybody agrees with that. Erwin Puts stated that it is better than 35mm Summicron non APO, and equally good as APO version on f5.6-f8.
But for M mount lenses Summarit (35mm or 50mm) somehow I don't see many praises. Are those lenses the same in lens design as Minilux lens? Sub question: same design is for f2.4 and f2.5?
I don't know about the Minilux lens but the 50mm f/2.4 Summarit is a classic, six elements in four groups, design with elements arranged like those of the Zeiss Planar.
Summarit-M series have 35, 50 and 75. All three are different from each other. 50 is not ASPH, 35 is. And comparing to Leica film P&S they works.
I have 35 2.5 since 2015. Best lens I used so far to have negatives for darkroom prints. Color and digital works too.
I wouldn't draw any connection between lenses which are named the same. Here is Panasonic made Lumix P&S with Summarit... zoom.
There is/was a 90mm as well. Leica recently discontinued the entire Summarit lineup.
They are great lenses, I have the 35mm and the 75mm and use the 35mm for almost all of my shooting. There is lots of praise for these lenses online. I'll see if I can dig up some of the links I found while doing my research before buying.
Actually I have 50mm f2.5 LTM Color Skopar, did not had a chance to test it right, with the current situation. I can compare it against Minilux, it is 40mm against 50mm, but f stops are similar.