Can't remember exact details but the 'wind up' method has some limitations and will produce errors for some calcs you have to do for CPL. As stated, sooner you get to grips with wind down the better. You were taught wind up for PPL because you generally have a known wind and only need to calc drift and groundspeed - wind up is fine for this.
There is no reason why you can't use any wizz wheel to do the exam with, so long as you can do all the calcs required. However, the man who wrote the exams used a CRP5 and therefore the answers you get will be closest to the exam answers if you use one too. Not that the other computers aren't right - but this an exam, not an exercise in producing the right answer...