It's a mag cased saw (not a clamshell) and will smoke a MS362 (I know that isn't saying a whole lot). They also mod extremely well and are tough as hell. A modded 590 will keep up or exceed the power of a MS400. I have both.A bunch of idiots hype them up on th internet and all of a sudden they are gaining market share from the other two? Back to reality...NO.
The CS620 version is their pro version that comes with better porting, 2 rings, unlimited coil with more aggressive spark timing curve and a bigger carburetor and runs with a MS400 right out of the box for 400 dollars cheaper. If you haven't tried one out, you should. Damn good value.