I've just ordered a Garmin GTU10. I saw somewhere else that someone was using one on a Phantom. They had it strapped to the legs. Once it arrives I'll test it in anger. I live in high mountains with large forests so should be able to put it through its paces. Like any GPS it needs line of sight to the satellites so won't be infallible.
I have another use for it in that it would be handy for the wife to keep track of us when I have a Motorcycle Tour out so my dinner is ready when I get back
If you can hold on a bit I'll let you know if you are wasting your money.
Battery life seems good, as does accuracy but I will try it in some nooks and crannies. The service charge appeals compared to many others. It only gets knocked down below 3 other makes in reviews because it can only record tracks for up to 7 days. Not being someone who disappears of the face of the earth for weeks on end that is of no importance for me.