I built my car MM but built up a RM gearbox assembly at the same time so I could swap between the two quickly.
I tried mine in RM when I went to a soaking wet Kidderminster to see the difference just swapping layout made .... there were no setup changes other than correcting ride height (car is cleverly designed so you don't even need to get the camper gauge out!
Car was easier to drive in slick conditions in RM but once you got you driving adjusted was just about the same pace in MM. Can change between the two in 5 mins so long as you have the soldering iron warming as you pick up the driver
All other running has been MM.