The 50/2 DR lens is my all-time favorite 50 for Leica and maybe my all time favorite lens. The sharpness is terrific but the more moderate contrast and seemingly beautiful "micro-contrast" is superlative for B&W work, at least mine. I got mine with goggles for only $350 due to an aesthetic flaw that has no affect on its use or performance. The one you're looking at is a gorgeous example but personally I think you can find this lens quite a bit cheaper with patience.
As for "better" than the 50/2 Planar? Not better but different. I use a lot of Zeiss glass and it's terrific, more contrast and punch typically. Definitely more "3-D" look. I have the M-mount 35/2 Biogon and love it as well but the character is quite different than the 50/2 Summicron-DR. If more contrast and pop, especially for color work, is a priority then go with or stick with the Planar.
A couple of 50/2 Summicron-DR examples of mine:
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