Not sure why a discussion of the circular slide rule should automatically lead to a discussion of GPS.
The slide rule is for ground use. A GPS is used enroute. The two are not related.
I am convinced that the slide rule should be abolished and the time put to better use. Anybody who can afford to fly can afford to buy an electronic version for the wind calcs. The CRP devices are actually very expensive for what you get. The multiplication/division side of the slide rule is (in most hands) just a disaster looking for a place to happen and a 5 quid calculator does a much better job. The pilot then has to remember a few factors like 3.78 (USG to litres) but he has to remember those anyway to do a sanity check when using the slide rule.