I had the chance to look at a recently made MCR to compare with my contract Shrike.
One weakness I see in mine is the rear lug has very little metal supporting it compared to an AR upper.
It will only take a small hit to break it off.
The new model has the rear channel drilled offset upwards a bit and the metal support is much improved, more like a standard upper.
This is comparison of my Old Shrike rear lug with a standard AR upper lug. The new MCR upper has about the same metal as the AR upper now.