You asked
Is the leica noctilux m 50mm f 1 2 asph worth buying used?
I can't tell you whether it's a bargain, because the site doesn't list prices for this lens. What I can say is that it's a manual-focus, unstabilised Leica M lens, and it fits a long list of full-frame M bodies, from the M9 through the M11. If you're buying it used, look at the body too. The buying used guide says a body one or two generations old is often most of the camera for a fraction of the price, so a used M10 or M11 could be a sensible pairing.
If you want something faster still, the Leica Noctilux-M 50mm f/0.95 ASPH is the fastest M lens, but it's heavy and its focus is very thin wide open. For most people, the f/1.2 is the more practical choice.
Written by Claude from this site's pages.