I can't speak to the 8 rounders, but I have Ed Brown and Checkmate 7 rounders side-by-side and they are clearly NOT the same magazine. The Ed Brown magazine body is made of heavier steel than the Checkmate, has slightly different feed lips and a coated follower instead of bare steel. If Checkmate makes them for Ed Brown then they're using different specs for Ed Brown than the ones sold under the Checkmate name.
For what it's worth Ed Browns standard 7 round magazine used to be just a re-branded Metalform with a rounded metal follower.