I have been using a Pilot 111 for a few years now, and for route flying I have found it accurate, easy to use after a few flights, and a great help when VOR's are out of range. It is also a great reminder when you stray off your VOR track or heading, even for a few moments.
I find it is not much good at keeping you out of controlled and restricted airspace. This may be a poor data base, or poor depiction of the airspaces, whatever, I don't use it for this purpose.
The other real danger is in inputting user waypoints without verifying the accuracy of your input.
It is a great DME back up and the only one if tracking a VOR without DME facility. I invariably set it on map mode with the DME info on the side bar.
Hope this helps.