I learned to use a prong when I took my 66lbs male GSD mix to a trainer when his dog reactivity was too much. This trainer was experienced in training dogs in the air force for some +20 years, and he taught us to use a choke first, then a prong.
But I have quit the classes after some time, since there are things that I don't agree with the trainer. Corrections that are too harsh, dominance theories (dog looks at you = dominance; dog lays down when you say "sit" = dominance = requiring correction), and focusing too much on repressing rather than dog's insecurities were some of them. Also, he cannot understand why the prong is not working as effectively for us as for him.
Problem is, when it comes to prong corrections for reactivity, if not more intense than the reactivity itself, is only good for feeding the attack drive. There are some bite trainings that do use prong to motive more bite from dogs. But my trainer can successfully cut my dog's reactivity at any level, since he's the master of punishment, that you can notice the difference between him and common mortal noobs like me and other people when issuing corrections (timing, posture, attitude, all are very intense and domineering).
I'm not trying to paint him as a cruel person, just stating the reason why prong often worsens reactivity, coz most of the average owners are not skilled enough to issue corrections intense enough.
I guess that many prong users already are aware about this and don't use prong for reactivity anyways.
But I do use prong on my dog, as it still keeps his reactivity to minimum and gives me control that I can't get with any other tool I know. I don't see it as a cruel tool, it does issue pain and discomfort, but it all depends on how you are doing it anyways. It would be great if I don't need it, but I use it if I see the need to, and I won't care for how people judge it. At least now we can walk past another dog with just some growls, but rarely jumping and barking anymore (and I rarely need to correct, but rather encourage him to continue going forward).
To be fair, I've tried halti head collar, and it was a disaster. My dog never got hurt for using a prong but he got hurt by using a halti. It happened when we were passing by another dog and as I tried to pull his muzzle away, he started to fight the collar and scratched and bit angrily out of frustration. It left him 2 scratch wounds on the muzzle. I concluded that this tool can be much better for desensitization (it worked well when another dog was at a considerable distance, and it was a gentler solution and definitely won't escalate reaction like prongs), but it is not safe to use it outside a controlled training environment, due to the dangers when passing threshold.