Can't help much on the Elmer-M 50/2.8 vs Summarit-M 50/2.4 issue. I've not had the opportunity to use either of those two lenses.
I have a Color Skopar 50/2.5 and a Summicron-M 50/2 (current series). Both are excellent lenses; neither is overly large or heavy, but they're not "pancake" flat for sure. I've not done any specific direct comparisons for sharpness or whatever, but they do render somewhat differently, and the differences are pleasing for both of them.
The CS50 works better on film than on digital sensors; there's a small bit of color shifting across the field on most FF cameras' sensors. For the Summicron-M 50, it doesn't seem to matter much which recording medium I use.
On the Leica CL's APS-C sensor, you can barely see any color shifting at all with the CS50
My CS50 has a tight, precise feel to all of its controls, no looseness or sloppiness. It feels every bit as well manufactured as the Summicron-M 50.
G