It’s a nice lens, no complaints here. I do like my Summaron better but there’s a big price difference. The Summaron is a bit sharper and it doesn’t stick out as far from the camera so I can pocket it easier. These were both shot with the Jupiter 12:
It can be finicky to work well with Leica rangefinders. Mine, a 1955 chrome finish (aluminum, actually) required shimming to get proper focusing with my M4.
I had one as the first lens on my Leica M4, and finally (stupidly?) sold it due to its' 2.8 "limitation".
But it is a very capable lens (flare can be an asset or an issue, depending on your subject), the aperture is a bit touchy to poperate but mine had a "broken" filter screwed in so that the handling was easier.