I use, used both when shooting professional= getting paid, I have a number of R system lenses as well as several M system lenses. I am not an expert in optics, I think I can judge a good image. My R lenses are comparable to their sister M's and unless a client specifically stated, M's, I would inter change between the two. Also the R system being based on a single lens reflex camera produced many different lenses that Leica M could not. Bottom line no difference really.