have seen this mentioned before, and if it works then great,
but,
if it dont, then thats £60 down the swanny,and still need to lay out £100 on a proper one,
plus its locate only, so if it does get you above your fert, you still dont know how far down it is, a foot or 15 foot?
means having to dig slower, save cutting your fert in half with a shovel
think for the extra £40 Id rather know the depth too