I've never seen a match grade BCG before. That said, I'd never of match gas blocks either until I saw Rainier's and understood how their gas blocks are a better fit to their match barrels. If I wagered, Rainier had their BCG machines to higher tolerances for a precise fit in their upper receiver. Likely their bolts are headspaced to their match barrels too.

Looking at the review of that one in particular and I'd keep away from it. Not sure the story there.