Thanks guys,
Since my last post i've tested this light at depth (12m) successfully and completely resigned the QTC system to stop there being any battery crush.
I'll elaborate on this soon and hopefully do a video too as the QTC function is pretty smooth and has been for many months.
Peter, you should patent your QTC module and then sell the design to the leading flashlight manufacturing brands.
To my knowledge, none of them have succeeded in making the QTC have a smooth function.