I will simply say that I agree with what Flying For Fun has said.
One other small point is that pilots IFR and VFR must remember that even the approved units are only certified to keep the flight within 5nm of the centerline (RNP5) so no point in planning to miss a CTR boundary by 1nm based on GPS.
Also, I have come across plenty of pilots who use GPS in one form or another. Of that large number, less than 1% knew what RAIM checks were and when they are required and even less actually did a RAIM check pre-flight. In this area, Eurocontrol and National Agencies could do more to publicise the tools available.
Regards,
DFC