There's an old saying: "Good, fast, or cheap -- pick any two." While it may hold true for most things, I believe the 50'Lux could well be the exception to that rule. Although it isn't exactly cheap, it is certainly affordable, or obtainable, if you really think you want it and willing to save for it. With a max aperture of f/1.4, it definitely fulfills the name that it was given ("summi" = maximum, "lux" = light), and it's only bested by the Noctilux ("nocti" = night) in the Leica line of 50mm lenses. Just how good is it?
Other Leica lenses have been marked as APO (apochromat, like the latest 50mm APO Summicron), and FLE (floating element, like the 35mm Summilux ASPH FLE), because that's the only way to distinguish the lenses from their predecessors. You will be happy to know that this 50'Lux is both of the APO and FLE design. Many will say that they prefer the old lens rendering from the designs of Dr. Walter Mandler, instead of the more clinically modern designs by Peter Karbe, current leader of the Leica Optical Design Team. However, you'll find the 50'Lux still retain some of the old-world look while producing amazing sharpness, and that's probably why it's crowned the "best 50mm lens ever made". It's a lens to own for a lifetime, for sure.
Final note: if you wish to shoot wide-open during day time, consider buying a ND-filter, which I have already documented [HERE].