This is from the perspective of a 2018 Ripcurrent S (RCS) owner
Everything "hardware wise" on the RCS is a step up from the Rover.
52V power system (less performance loss when the battery starts getting low on charge), much bigger battery (RCS=998 watt hours vs Rover=672 watt hours) , higher peak motor wattage, Speed pedelec capable, hydraulic brakes, 9 gears instead of 7, 3 frame sizes vs 1 sized fits most, and the RCS comes fully set up for commuting (fenders and rack included). The RCS uses a torque sensor + cadence for power delivery vs. a 12 magnet cadence sensor on the Rover. The RCS comes with a thumb lever throttle. The Rover comes with a twist throttle with a throttle cutoff button.
That said, parts are far more expensive on the RCS. Battery replacements for the RCS cost $1300 vs $550 for the Rad Rover. Unless you are familiar with taking care of hydraulic brakes they are harder to maintain and require some
specialized tools to bleed (replace the brake fluid and get air out of the system).
If you have dealt with maintaining a "normal" bicycle moving up to a Rad Rover will be pretty straight forward. If you have dealt with maintaining a mountain bike with hydraulic brakes the RCS will be pretty straight forward.
I'm not that familiar with the M2S so I can't directly comment there.
My RCS has been trouble free since I got it. I've put around 200 miles on it so far (got it late season and didn't ride it during the winter months) and the only thing I need to get done to it is have the brakes bled which is a regular seasonal maintenance thing. I did break the front fender on it but that was due to me being a klutz and no fault of Juiced bikes. The one specific feature I'm a fan of on the RCS is the cruise control feature. It is really useful for long straight stretches of road.