You asked
Is the leica macro elmar m 90mm f 4 good for product photography?
I think it's a good choice, with one caveat. The Leica Macro-Elmar-M 90mm f/4 is a macro lens, so it's built for getting close to small subjects, which is most of what product work asks for. It's manual focus only, so you'll set focus yourself. That's fine for objects that sit still. The site doesn't have a dedicated product photography guide, but the reasoning in Landscape applies here too: with a static subject and a tripod, you can work slowly and get focus right.
For bodies, I'd go with the Leica M11, the Leica M10, or the Leica M (Typ 240). All are full frame and fit this lens.
Written by Claude from this site's pages.