Personally I would say ground school at PPL level is best left to the flying instructor to brief before taking the exercise into the air. There is nothing worse than having to explain something in the air that should be done on the ground. Preferably with a whiteboard.
It also means that they only have themselves to blame when they inevitably miss out some of the more discrete (but vital) points!
My opinion, for what it is worth: save your pennies and go flying!