Nowadays, the name of the game is MILSIM realism. BW 4 gets you real steel Like ROF with full power when firing each BB in burst mode as well as in fullauto, even when run by a 11.1V high C battery. That is why Polar Star fusion engine can sell. But at a significant investment and inconvenience of carrying a gas tank in order to achieve real steel like firing mode!
The only thing that Polar Star fusion engine can give you extra is to change FPS range by changing the nozzle. But change of FPS can be accomplished by changing the spring in an AEG. With more and more quick change gearbox available, it is much easier to accomplish Polar Star kind of performance by upgrading an AEG at a much more affordable price and convenience!
Check out videos of Burst Wizard on You Tube
AEG Burst Wizard