I recently purchased a used Glock 17C for a reasonable price. I got it just as a novelty and possibly for Action Match shooting. Since I have been playing around with PCC and Open Division handguns with compensators I wanted to see what the Glock 17C could do. I was surprised how well the ports worked. I tried it with factory 115 gr and 9mm major load and did not notice a significant difference in compensation.
I was doing some night shooting and thought it would be cool to capture the flash from the vented ports in the slide and barrel. I shot a video in slow-mo with my phone. Then scrubbed to the frame with the muzzle flash and took a screen shot.