The Anarchy Outdoors Glock 17/19/20 Compensator is not compatible with a Glock 21.
No. Anarchy Outdoors does not recommend modifying the compensator. It is only listed as compatible with the Glock 17, Glock 19, Glock 19X, and Glock 20.
Yes, the correct model Anarchy Outdoors Glock 17/19/20 Compensators for a Glock 19 Gen 4 are MPN:791617487574 (Blue), MPN:791617487598 (Purple), MPN:791617487581 (Gold), and MPN:791617487567 (Red).
According to the manufacturer the Anarchy Outdoors Glock 17/19/20 Compensators are model specific. So the Glock 17 Gen 3 model will not work on a Glock 19.
No, the Anarchy Outdoors Glock 17/19/20 Compensator is not compatible with the Glock 40 due to the length of the slide, it would not allow for this compensator to be properly installed.
The Anarchy Outdoors Glock 17/19/20 Compensator is not compatible with threaded barrels. I would recommend the TRYBE Defense Universal Single Port 9mm Compensator, which is designed for threaded barrels, and can be found by using the link below:
https://www.opticsplanet.com/trybe-defense-universal-single-port-9mm-compensator.html
The Anarchy Outdoors Glock 17/19/20 Compensator is made from Aluminum and is designed to reduce kickback by up to 50% by pushing down the muzzle and redistributing gas pressure.