I have barely seen any RCR's or RMR HD's in the wild yet on pistols, and the Benelli M4 platform is pretty niche, mounting micro dots on Scalarworks mounts is even more niche. I'd buy from a company that has a good return policy, and place it on the mount carefully without mounting so you can decide whether you want to keep or return.
Steve, you are correct it will "Fit" however forend modifications would need to be made. I did not want to send someone down the path of buying a expensive barrel not knowing forend puchase and modification would needed. Thank you for all of your contributions to the forum.