None are really needed, i mean out of the box you got the shaft 4 (UPGRADE), it has the zick 2 (UPGRADE), OLED BOARD (Upgrade), Cure 3+ bolt (UPgrade),
Adjustable Every Were
Loudness but better after break in
Break in is 10-20 cases
This EGO11 is the only thing of its kind to have a solenoid thats adjustable to suit you, no other gun not matter how cheap or expensive can match this. The adjustable solenoid lets you control the flow to the solenoid on the forward and rear stroke which tuning around with those can do hundreds of things from gaining or eliminating kick, gaining or loosing efficiency, raising or lowering rate of fire and much more. To fully under stand the solenoid and how it has such great benefits you need to own one and then play with the settings your self. Every gun and every shooter is different. I have my solenoid settings at 1 and 7 and on my second case through the gun my shot counter says 1453 balls on a tank 68/4500 with 4000PSI in it with a ROF at 12-13 BPS.
The gun has a lot of on board features you really need and alot you don't. Its really up to you if you want to adjust it but its not nessecary.
The feature I like the best is the live graph that streams across the screen showing your BPS consistency when your rocking the trigger. The 5 point adjustable trigger with Optical switch or micro switch, the choice is yours.... I like the micro because it has an adjustment for its self compared to the optic were the rear and forward travel is the adjustment so its hard to fine tune it just right.
I would really recommend this EGO11 because its well worth the money if your really in to tuning and efficiency. My game play has changed dramatically ever since i started running this gun. My snap shooting is better, my off the break running, speed and lane'ing has all improved. This gun improved the way I play and performance just about all the way around.