1. LED Tracer Unit (Optional and Included)
2. Chamber Lock (Prevents BBs from falling out when you eject magazine)
3. Easy adjustment using new design dial for more stable hop-up

This set also includes a free MADBULL blue 60 degree SHARK hop-up bucking rubber.
Note that the chamber lock function works via an O-ring in the BB feed tube that goes up to the firing chamber. The O-ring prevents BB's from falling out of the gun when you pull the magazine out, which is normal in a Marui type gearbox. If you find this causes any problems for you, or you prefer that the 3-4 BB's in the feed tube fall out of the gun during reloads, you can simply remove this O-ring to disable the chamber lock function.

New hop-up adjustment dial stays in place and won't shift from vibration during full-auto firing, giving you more reliable and consistent hop-up than in traditional guns with slide-type hop-up adjustment lever.

And if you need one more reason to get this hop-up unit, Madbull tested this hop-up unit on the Echo1 M4 and got a 5% increase in power due to a better air-seal. So you get 4 benefits in one unit! Need we say more?