One person at Leica forum purchased whole bunch and tested them. Nobody was overwhelmed with their performance.
Bulky and no focus tab, except one. Meh...
New kid on the block is this strictly made in China 50 1.1, this is where gearheads are raving about. And it is really inexpensive for M-mount lens.
For those used prices you could get a used Zeiss Planar 50mm which is a much much better lens. I have not been impressed by the images I have seen w/ these Iberit lenses.