1/ What is the difference between the CS2 Pro and the Geo 4?
The Geo 4 and the CS2 Pro are immensely different, but some of the largest differences to them are that the Geo 4 utilizes the IV Core as apposed to the GP Core in the CS2 Pro, additionally the solenoid of the Geo 4 is adjustable, so you can tweak and tune the shot of the marker.
2/ Can the Geo4 be used in mechanical events?
If the event allows you to cap the marker at 5.5BPS then yes you can, however there is no Mechanical frame or conversion for the Geo4 at this time.
3/ What Bolt is in the Planet Eclipse Geo 4?
The Geo 4 uses the IV Core for a very smooth, reliable and consistent shot.