The circular slide rule wastes about 5-10 hours of the already scarce (and non mandatory) PPL ground school which would be better spent teaching pilots some operational tips on how to fly from A to B, how to use the internet to get weather, notams, etc.
More practically, the accuracy improvement through using the circular slide rule for wind drift etc, over a rule of thumb like "max drift is half the wind" is less than the typical error in the winds aloft forecast.
The calculation side of the circular slide rule is totally pointless, and is very error-prone.