Magnetic Sensor trigger
For me, none.
This review is based on MY experience with the MINI. Nothing else. Out of the box it looks and feels great. After having used any other gun you can barely feel it in your hands. The trigger is different from most magnetic triggers in that it uses magnetic repulsion to return the trigger. Dont be fooled by how big the the fore-grip looks in the pictures. Its only a little wider than a 9v battery. I haven't had any chopping, board, or leak problems with my MINI. For the month that I've owned and shot it, its performed flawlessly. Upgrades are preferences only.
The perfect paintball gun. Its the lightest gun ever made. Very fast and all you'll ever want for a great price.