Cirrostratuss
The "faults" you list are not equipment failures.
The first is the result of not reading the user manual. And then flying with the unit for real before making sure it works as desired.
The second is the result of a poor signal - if using a handheld in a metal cockpit you should always use it with a window-mounted remote antenna. This is a common problem. A radio won't work very well in a metal box (with some holes in it) and a GPS is no different.
One could argue that there should be a ground course on GPS usage, and I would agree. But, having been to one such course some years ago and been the only one who turned up, I suspect there would be very few takers. The vast majority of GPS users are completely at home with gadgets (and have no problems working them out). The rest are probably too small a customer base, especially given there is no mandatory ground school in the basic PPL.
I think the OP was after views on equipment reliability, rather than the likelihood of mis-nav with a GPS versus other means. My view is that GPSs are on the whole far more reliable than other avionics, and also it is far harder to be misled when using them for navigation.
In 6.5 years of aircraft ownership, I have spent $1000 on a new LCD for my KLN94 GPS, and I am about to spend $3200 on an exchange KI-256 horizon (which costs $11,000 as a standalone buy - and these are prices direct from
USA). The overall pattern is that general avionics expenditure is an order of magnitude higher than GPS related stuff.