I'm using an 'old style' Vertex for underground work, with a Stenlight attached to a normal blade mount riveted on (it's AR's old helmet!), and haven't had any problems at all with it losing its settings. I do have a little concern about the lack of forehead protection, as the cradle is right against the shell. Although I did once drop a rock on AR's head in a mine and he was OK afterwards. So it's been tested.
Sensibly, I use the new style Vertex Best for rope-access, and it is very comfy, and far better balanced in terms of the cradle/shell placement. Again, no slippage. As I had to work in an explosive environment recently, I got the lamp designed for the slot, the Pixa 3, but it's pants. Front-heavy, due to the integrated battery, weak as **** compared to the Sten, occasionally falls out of the slot (!) and the settings on that change constantly too! But that's another story...[i]