Well err yes, I did use my CRP1 to calculate the new heading for the diversion on my NFT, but I wouldn't dream of doing so now.
You have just been given one method of quickly getting the corrections for the new heading and there are plenty of other simple methods.
I had to do a diversion (re-route) to the Isle of Man on Saturday morning because I couldn't get over the Pennines in a PFA (VFR-only) aircraft, and I certainly didn't use a CRP1 or any other calculator.