I have the 129 and 100. Happy with both so far. I won't hesitate to get the 104 some day when I need one.
The 129 did come loose once, but I keep it tighter now, and it hasn't come loose since.
My only gripe is that once the mount is tight enough, the "QD" feature is useless, as the lever is too tight to flip by hand. Not really a big deal though. I re-zero an optic any time I remove/replace it anyway.
I still haven't seen any evidence, yay or nay, about whether the Larue partial crossbar gives adequate engagement on the XCR center cut rail. I will check that with one of my existing mounts before ordering a dedicated Larue mount for the XCR.