Agency Arms states that this compensator may require tuning of your recoil system. My suggestion would be to use the compensator with the standard ammunition you use, if you experience malfunctions, then I would recommend changing to a DPM recoil system.
Yes, this Agency Arms 119 Dual Port Barrel Compensator will be compatible with your FN 509 Midsize Tactical pistol.
The Agency Arms 119 Dual Port Barrel Compensator was designed for the FN-509. I would not recommend using it with your Glock 48 as it will not fit flush with the slide and may lead to holster compatibility issues. I would recommend the Strike Industries Optics Planet Exclusive Strike Micro Threaded Comp, found by using the link below:
https://www.opticsplanet.com/strike-industries-optics-planet-exclusive-strike-micro-threaded-comp-quad.html
Yes this comp is compatible with the FN 509 and tappers to the nose of the barrel. Sage Dynamics has a YouTube video on it that you can watch.
Yes, this Agency Arms 119 Dual Port Barrel Compensator is compatible with all models of the FN 509 with a 1/2x28 threaded barrel.
Yes, this Agency Arms 119 Dual Port Barrel Compensator is compatible with your FN 509C.
No. This Agency Arms 119 Dual Port Barrel Compensator will fit all models of the FN 509 without modification to the slide.