One thing that bothers me about the RMS system is that it removes some of the torsional strength from the front of the car.
Look at the unit off the car. There's only one little crossmember. If you grab the unit by the mounting points it would twist much easier than the stock K.
It removes the torsional load from the T-bars but the car is stuck relying on the flimsy core support to keep it from becoming a pretzel.

The XV unit has the second cross bar that helps prevent flex in the K. It's still going to move around on it's own but once installed it would lead to a much stiffer chassis.

Adding the other pieces to stiffen the vehicle would really help either setup but if you're going that far you wouldn't consider the RMS in the first place.

I don't have any experience with either setup but understanding physics and knowing how to break stuff makes me lean more towards the better designed (and painfully expensive) XV.

If you're going to go drag racing, RMS has got the better looking product assuming you've already got a cage with forward bars.