Hello KayPam,
You have to check with your local CAA for which tools you are allowed to bring to the exams. In Germany, you are only allowed to bring to the ATPL exams pens, pencils, ruler, and a flight computer (ie. Aviat 617). They provide notepaper for calculations as well as a REALLY SIMPLE (read: non-programable) caculator. You probably would find the 617 more useful than a CRP5 since it also has MACH numbers on it. Once you pratice with the 617, you have an answer faster than with an electronic calculator esp. wind calculations, PSR & PET are super fast and easy, calculating MACH with IAS and different temperatures is a snap, etc. As for real world application, my IFR FI also flies executive jets and uses his almost daily to double check the caclulations he receives from dispatch.