I;m with Cobalt on this. I have used the Wintec gps logger
I introduced it on the dual navs. The students were keen to compare their evaluation of the flight with what the logger recorded. It does more than follow the track you get ground speed and altitude.
My students have liked having the device sit there passively and look forward to seeing how well they did.
For what its worth I first came across it on the TopNav competition run by the Royal Institute of Navigation. where its used to determine how well the teams complete the task.