bose-x - uneducated tosh - Really. Well I refer the honourable person to the CAA Safety Sense Leaflet entitled 'GPS' which in its opening paragraph states:
GPS must not be relied upon as a sole navigation reference in
flight-critical applications.
If you're using it at FL whatever it is in a light aircraft it should have been approved to BR-NAV standards which is the +/- 5nm 95% of the time. Instrument approaches require a higher standard of approval of GPS equipment.
Furthermore, my point is that a modern instructor who tells a student he can go and use his handheld GPS to fly an instrument approach or to use it as a primary means of navigation without it having been approved to do so, is not doing the student any favours.