I've not tried an RM20 but may buy an RM22 one day, and I wish they all had the boost.
GTO the Judge, my verdict;
Correct me if I'm wrong, but I assume the goal was to capture the coveted Marshall overdrive/distorted tone. Classic Plexi/modded Plexi. Not modern JCM or JVM, and not any clean channel. The (distorted) tone by which all others are 'Judged'.(for me anyway).
It definitely achieves this for me. Probably does it better than most Marshalls, especially since you can have it at low volume. It doesn't do 'Marshall' clean, and it doesn't do (modern)metal. But I can get those things from the other Lynch modules.(that is until they discontinued 2)
What it does do, is like a revised, better, warmer, punchier, higher gain version of the Brahma with a clear emphasis on classic Plexi/modded Plexi mid to almost high gain distorted tones. Without the clean capability of the Brahma. Even with the gain at 9 o'clock I have as much crunch(a bit thinner though, on low gain) as the Brahma at noon.
I've lost count of how many posts I've seen over the years wishing the Brahma had more gain. This is it! There's a definite change in the EQ too.
I have no regrets about buying it, infact I'd pay double for that tone. It's that good!....IMO