As above, the Magni Valve/Fly ram allows the A1 to be run at a lower operating pressure adding efficiency and reduces kick
There are 3rd party circuit boards available including the Rabid board from Rabies on these forums and triggers from Raguba.
There is also a front reg adaptor available from CP allowing a CP or any std ASA threaded screw in front reg to be used.
Oh, and 3rd party barrel kits too, though the std barrel kit is as good and as light as most, if not better.