There are only a few that are really available. Trigger (magnetic kit), Billy Wing bolt, Lurker Eigenring and an OLED Board. Depending on what format you play (PSP, Semi) the trigger might not matter. BWing bolt is supposed to make the gun smoother and more efficient. The Eigenring is also for efficiency. OLED boards are for super fine tuning and makes lives easier by not having to open the grip and count blinking lights. its all preference though. on my Dm13 I have a Virtue OLED and Billy Wing bolt.
MARQ Virtue OLED for sale!!!