A big, heavy pistol; most comfortable in large hands, this weapon is not for the faint of wrist. It runs on CO2 so while it clocks in at a very reasonable 330 fps, it kicks like a mule on steroids and its probably as loud as one too.
Metal upper with polymer frame, this is no plastic toy; it has the mass and weight distribution to make it feel and move right in your hands, it has nice crisp switches, trigger pull and mag release to make it perform with the best of them. The rail top is indeed 20mm but the curved beveling around the edges means that it will not necessarily fit all rail attach type optics so it will take a little trial and error without the right interface adapter.
With 21 rounds and 340 fps, it is no snub nose pocket gun either; it will not be the most powerful gun around but its about as powerful as a pistol can be for short range use before you start to get complaints about excessive force. With CO2, it hardly chokes on gas flow either; it shoots very stably with clean strait lines over close range. The fixed iron sight is good enough but if you do manage to put a red dot on it then you have yourself a corridor clearing compact cannon.