Based on looks and the video, it appears as if the PSA offering uses a regular AR15 7.62x39-bolt/carrier/upper versus the CMMG which has an oversized bolt/carrier/upper to accommodate the fatter x39 case.
The bolt on the PSA is 9310 steel, so they are obviously going with a tougher material to prevent it from cracking like a lot of the standard AR15 bolt heads made to fit the x39.
But the CMMG Mutant I think has the edge in durability being a shorter .308 sized gun.
The PSA has the edge in modular design as it uses a standard AR15 upper group.