In my opinion, the Equinox 800 is probably the best choice as an all rounder. A PI detector, best suited for gold will do his head in chasing relics and coins.
The Equinox is probably one of the better VLF's for handling mineralised ground when chasing gold due to its true multi frequency operation.
However, the real answer is to buy both a PI and a VLF if he's serious about chasing gold and coin/relics