SC, I'm a certain as one can be that 15 mins with a CR book & any competent instructor would be off and running. Hell, I learnt to use mine myself before I had IR or instructor ratings. The wind side is the major difference but it's not difficult, per se. There's an extra scale or two on the calculator side, but they help short cut some of the Mach No questions compared to a CRP.
WRT to there being very few, perhaps thats because the instructors only consider the CRP? Sort of makes it a self fulfilling prophecy.