I ran rapid rise XTR derailleurs on my mountain bikes for years and never had any problem with them. I used them with regular shifters that had no gear indicator(if it had one, I took it off). This was back in the olden days, when mountain bikes had front derailleurs, and it just seemed to make sense to have both shifters work the same way. With rapid rise, the thumb shifter always shifted to a higher gear and the finger shifter shifted to a lower gear on both sides. It just seemed more intuitive to have the shifters perform the same function on both sides.
With a low normal derailleur, the left thumb shifter would shift to a higher gear and the right thumb shifter would do the opposite and shift to a lower gear. This was especially hard for new riders to figure out.