I still use my Jepp CR5 (CR5 is the smallest one) after well over 25 years in things from piston singles to turboprops. With modern avionics I find I use it less but there are still some things I can calculate more quickly with it than by twiddling knobs & pushing buttons. Try calculating PNR or Crit Point with a GPS. Damned if I've figured out how to but my whiz wheel does it easily. Flying air ambulance over the N.Sea I used to have to do those calcs regularly. With my CR I could also use off-track DMEs to find along-track groundspeed - quite useful when out of range of on-track DMEs.