The way I read it, the Magnum and Standard have differing port angles. The Standard is designed for smaller cartridges and is geared towards reducing muzzle rise, whereas the Magnum is recommended for longer cartridges and somehow differently tuned to specifically reduce barrel whip. It appears as though there are only the two bore diameters, .300 and .338.
The cartridges in the middle of the range....308, .300WIN, etc...can be used with either version.
You've gotta read all the ad copy and watch all the videos to even glean than much info. I love the ultralight weight, and the reduced muzzle jump with the standard model sounds great. Since they never mention it, I am assuming that this will be one crazy-loud brake, and that alone will steer me away. I'm not recoil-sensitive, but there are lots of braked guns with such an increased level of muzzle blast experienced by the shooter that it completely negates any other possible benefits of the brake IMHO.