Holy crap that is cool, I want...actually I bet I can build an equivalent for less. I wonder how easy it is to source a emf transmitter (and receiver) with range of a mile.
Don't know much about EMF, but check out the equipment being used for FPV flying. Should be simpler given that directional antennas could be used.
But I think the system being sold has some built in stuff for tracking each shot.