It says 'pump action' in fire mode. that should make it pretty obvious. If you are ever unsure of something try it in the VR first if it feels right start the trial and use it in combat.
Well, you need to click the button more. Sustained simply means it can keep going, which, in this case, means it doesn't have to stop to reload as soon.
It technically has a faster reload and larger magazine then the Deimos, but only by a very small margin.
