Interesting mount to be sure! I have a similar one on a Browning GP, but it mounts on the left side rather than the right. It is a plus and minus cure. As you noted, it mounts without having to alter the original gun, which is a BIG plus. The minus side is a frame mount on a semi auto depends on the barrel lock up to frame position to be consistent and grip mounts alter the feel of the gun.
As a side note, a forum member here offers a red dot solution that replaces the rear sight, something I prefer as it gets rid of the two minuses I mentioned above while maintaining the plus of not altering the gun. Be that as it may, that Leupold mount is rare in itself and is a noteworthy item.
Nice find!