Rapid Rise Rear Derailleur

I still cant figure out how these work, there are some people that are fans of them in the mtbr forum postings from 2011, so they've been discontinued for some time now.

Is it correct the spring is reversed and that leads to different finger shifting?

Youtube came up with one video of a guy going through the gears, camera only showing rear gears and der moving.

Yes, the spring pulls it the opposite way, into the low speed gears. Works with any shifter of the proper pull ratio. For trigger shifters, you hit the thumb lever to up shift, and the trigger lever to down shift. Rapid rise is a little bit trickier to adjust cable tension.

In concept they're a neat idea. As said above, finicky with cable tension. They don't work very well with anything less than perfectly clean cables and housing and a healthy drivetrain. Once the derailleurs develop any bushing play, the shifting goes to crap. That'll happen eventually with standard derailleurs too, but they can last a lot longer and still shift very well. Basically it's a system that works as engineered, it just needs twice the maintenance.