I'd just like to jump in at this point, firstly i'm in the UK living on the North Devon coast and detect the huge sandy surf beaches we have locally.
I have an Equinox 800 with the 15" coil and a Whites TDi beachhunter and have had them 18 months each detecting 4-5 days a week.
Yes the Nox is deep but I find the TDI much deeper. I also find that on my benign sand the TdiBh is deeper with ground just clicked on and running full gain and delay set at 15.
Just before Christmas I had 2 platinum rings of 11g and 12g, both giving high tone.
I am in fact yet to get gold or platinum giving a low tone. I find the TDiBH just if not more sensitive than the Nox on small stuff and regularly dig earring backs and very small gold.