Essentially I have 3 speeds: climb (including take off and go around I.e. full power), cruise, and approach. Each of these can be set quite accurately by rpm/MAP gauges, possibly even to within 3-5kts in cases of Vfe. This of course relies on having at least 1 or 2 hours on type.
GS is almost pointless for the visual approach and landing, but obviously much more relevant for navigation. Finding GS using good old fashioned timed distances will do. And actually from the timed distance and cruise rpm/MAP setting, a headwind/tailwind is easily calculated. Couple it with the applied drift calculation and you have a good enough wind direction also. This could take 15 seconds or so maybe?
I think these calculations are so basic that in the cruise a GPS GS may as well be used as the primary rwference. One would quickly notice if it was unacceptably inaccurate and revert to the proper methods of flying
(I jest...
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