I switched to a Meg DSV, but I did a little mod for my buddy to secure his HUD mount. I don't suggest you try this if you are not mechanically inclined, good with measuring, and accurate with power tools. I drilled a hole in the interior radius of the HUD holder only about 3/4 of the way that was tight enough to secure a s.s. dowel pin (I believe I used 3/16" diameter). I then drilled a matching hole in the DSV but slightly larger so it would slide in easily. This was done on the outer part of the HUD holder so it could be fitted and then clipped on the rest of the way. Never moved on him again.
^ this. I bought that unit from Don and that is the only HUD holder I've had that didn't move around. A brilliant mod, if you have the mechanical ability and tools.
I still have that clip around here somewhere. It didn't fit on the rEvo BOV, so I quit using it a long time ago. Now that I'm back to the stock DSV, I need to find it and see if I can use it with my NERD.