Regarding support for Holosun sights, we don't develop nor make plates for Holosun or other Chinese made sights.
While 407C and 507C sights can work on our RMR plates, users can't use our T15 6-32x3/8 sight to plate screws, this is further explained here: RMR sight to plate screws vs. Holosun screws We specifiy 12 to 13 in lb for sight to plate screws, though these T15 screws can be torqued north of 20 in lb, Holosun uses mild steel screws and are not nearly as robust. Do not use our RMR sight to plate screws on Holosun sights.
508T is not recommended for use with any of our RMR plates. Every single 508T we tested since 2020 (save for one we tested in 2023) has been a loose fit on our RMR plates, which are designed to hold the sight immobile prior to sight to plate screws being installed and toqued to spec. If they can't do that, it's only a matter of time before the recoil loosens the screws.
509T footprint is incompatible with anything but Holosun sights, the recoil lug height is less than 1/2 of an Aimpoint P2's. EPS/507K is essentially a 2 lug version of the 4 lug RMSc footprint. None of the plates we make will work with these sights.
FCD is a US company, we support sights made in the USA or allied countries. https://www.vermilionchina.com/p/holosun-chinese-or-american