Got a chance to install it this morning. It's rock solid!
Not liking that self-tapping screw you're using. I can already feel it wanting to strip the hole. Go with a standard wood screw, they seemed to work well on your previous design, for holding on those side supports. I would also go with a Phillips screw since many field tools like Gerber/Leatherman/Swiss Army knives and such don't have a Robertson build in.
Reduce the length of the groves. Right now they go right up to the bottom of the supports. I see these as fracture points. Shouldn't sacrifice mechanical strength just to have cosmetic groves that mimic the mag splines.
Also extend the front support further back. There is a bit of a gap that will allow dirt to get in. Front corners could also use a bit more material to close the gaps.
I will put it through it's paces at the next SR match...