Received mine today, fit and finish are excellent! It feels like a quality piece of hardware. Fits snugly to the rail and flush with the trigger guard. The fact that the Allen key was long enough to clear the end of the weapon was a nice touch (unlike another adapter I could mention).
Checked the fit with the Viridian X5L Gen 2 and X5L Gen 3.
The Gen 2 fit with very little gap to the trigger guard (and I didn’t need to re-zero it). The Gen 3 fit perfectly, with no gap at all.
Thank you to @Sextus and @gator33 for a superbly executed project all around and the machinist for quality workmanship!