I've owned several "C" model Glock handguns (still have 3), and have had no problems at all with them. Ported Glocks are just as accurate and reliable, but may require more frequent cleaning, as the porting runs through the barrel and slide. Some of the hot powder gasses squirt through the barrel/slide gap and swirl around in the frame, dirtying things up a little more than normal. Other than that, great guns!
For range use, I buy the cheapest range/target ammo I can find. The ammo manufacturers do not add flash retardant to the cheap ammo, and when combined with the reduced lighting on most indoor ranges, you can get a spectacular flash from the porting when fired! With modern self-defense ammo, you will see almost no flash at all.
My G19C with cheap target ammo (snip from video clip; best way to capture pictures of port flash):