You are the pro and I should listen. Should. But I have an old M8 that is great in mono. The M9 and M240, too, but the M8 seems a bit more authentic. I shoot both RAW and JPG but use just JPG. I am just about as lazy as a man can be without an iron lung to breathe for him so JPG is great.
I understand I can go through the RAW > mono conversion but for my amateur eyes I do not see the advantage over letting the camera do it. And, also, I am not out there competing to sell images so can be way more relaxed. Oh, wait, Pixii shoots RAW mono. It is often good. I have not shot PIxii in a long while. I'll have to find it, upgrade the software and shoot some RAW mono to see. You always find work for me. ;o)