You can be very lucky with any Jupiter lens. I own a J-8 and J-12 resp. F/2,0-50mm ; F/2,8-35mm and to be honest the difference between my Leica F/2,0-50mm Summicron and J-8 is not that big .......

And also that little J-12 has amazing optics. They are calculated according old Zeiss lenses design. J-12 is a Biogon type with the last lens element very deep into the body hence you can not use this lens on every LTM camera. The most important thing is to use a lens hood on these type of older lenses.