The circular slide rule is a relic from WW1. It is taught because we beat the Germans with it (twice actually) so it must be the "proper" way to do flight planning. My grandfather went down the coalmine and my father did too, and YOU will too, my son.... much if aviation is like that, which is great if you don't want too many of the great unwashed coming into it.
Like the signals square, the overhead join, and a load of other cr*p.
It's a complete waste of time. It cannot be used in flight, unless you have a plane with an autopilot, and if you have one of those, as I have, then you will be navigating with more modern methods anyway. Women (who can do two or more things concurrently) might be OK with it
The time spent (wasted actually) learning how to use that damned thing would be better spent teaching how to use quick rules of thumb (which are just as accurate, given the typical error in the forecast, but your instructor won't tell you that - even if he knows it), and how to use a GPS. And use a decent flight planning program like Navbox. Come to think of it, Navbox Pro costs only a bit more than the CR&P-1
I've done the FAA IR, and done the FAA PPL before that, and the FAA (which looks after a GA fleet about 10x bigger than the whole of Europe) doesn't require it. Some of the US instructors like it for sure but it isn't a requirement. You can use a PDA running an E6B sort of program if you want.
As for Navbox, no it doesn't provide (useful) vertical navigation, nor is the map quality and information content good enough for CAS or terrain avoidance. In Europe, they would have to increase the price an order of magnitude to pay the mapmakers' license fees (the VFR and IFR charts are free in the USA) so you have to use the printed chart for these things. It's really no big deal. What Navbox gives you is a dead fast plog, wind-corrected if you like, and a simple map to print out.