It's early so bear with 🙂
The Abm models you can consider the flag ship, Class A/B solid state power amp (old school heavy type), Big, loud and versatile. They have a pre amp valve for a blended drive section and a fantastic and versatile EQ
The RM are the light weight equivalent, 300/500/800 watts Class D Lightweight Power supply, I'd describe as a valve emulated blended drive, Just as good EQ
Both have a useable one knob compressor, Sub octave generator for some nice lower end growl.
You can more or less get the same voicings out of each, it all depends on whether your happy to go big large and heavy or have a nice light weight amp.