I recently purchased an HK VP9 optics ready pistol. I am extremely impressed with their optics mounting system. Here are some pictures.
Everything about it seems well designed. The cover is secured to the slide with two beefy screws with a T15 head.
Once you remove the cover plate, this is what you see.
You then use the same T15 screws that secure the cover to attach the RMR/SRO/Holosun plate I purchased from the HK web shop. I ordered the plate from HK, and it arrived two days later, by free FedEx shipping.
Here is a side view of the installed plate — looks very stout.
Finally, here is the slide with the Holosun 507 installed. The Holosun came with four shorter and four longer screws. HK cleverly designed their system so it would use longer screws. Look forward to shooting it, but so far, I give this high marks!