Hi Keith,
I moved to the coast 7 years ago and started beach hunting exclusively.I took a whites m6 with me as that was the only detector i had at the time that was capable of hunting the wet sand.It was brilliant on the beach,the best single frequency detector by far ive ever used in wet sand conditions.
If the mx5 has similar performance your mate can't go wrong with it........i had plenty of jewellry with the m6,some of it at decent depths in the wet sand.
Shame he cant use a harness to support something a little heavier as a used explorer or similar would be ideal .