I've just reversed engineered the whizzwheel and now have a spread sheet that will generate the sine and cosine waves for drift and GS for any given predicted wind so I can workout the heading to fly for diversions in 2 seconds in the air.
I don't think one needs to use the circular slide rule when airborne. One is not allowed to use electronic calculators in the ground exams or in planning the flight and there is thus an implicit assumption that you will have no option but to use the slide rule, but I don't think you actually have to use one.
What you have to watch is this: the CAA exams have tricks to catch you on common errors and if you get the answer 1 degree out you will fail that question. The multiple choices are rigged to catch this. The fact that not even a £20k autopilot can hold a heading within 1 deg is irrelevant.
The trig for wind calcs is trivial. There are also countless E6B programs around for PDAs. I have one myself, called Flightcalc or something like that.