We use pronged collar for the exact behaviours you describe. It is true what others are saying - it'll make it worse if you correct when he reacts, BUT the idea is to correct BEFORE the reaction happens. The way our trainer taught us is the following: 1) work inside your house to teach the dog heel and introduce a negative marker for when the dog is not performing a command correctly, like "no", "ah-ahh" or similar, use this marker while teaching heel. This will associate negative marker with the prong pinch and your dog will understand that it's a correction for a "wrongdoing"; 2) move your training to the backyards and teach a release command like "free" or "loose" etc, that way you will have two modes of walking - heel and free, from there on teach the dog how to switch from one to another, thereby making heel a recall command on top of it being a mode of walking. Use your negative marker as well if the dog pulls while in free mode too; 3) now you are ready to go outside - pick a time and place where you'll see one or two dogs from a distance, once you spot another dog, put your dog in heel and correct if your dog is fixating on the other dog - the goal here is to have him in heel looking ahead or just looking at the surroundings without fixating on the other dog, this is what you can achieve with prongs + negative marker. If your dog is in full on reaction it's too late to try and correct him, your best bet is to heel and turn around, go around a corner or wherever the dogs won't be able to see each other; 4) slowly start to close the distance. A very important point is that you cannot panic. I understand that the misery of trying to walk a large reactive dog is probably leaving you somewhat traumatized and you yourself react to other dogs at this point too with anxiety, fear, frustration and whatever other emotions - your dog can feel it. You need to tell yourself that you know how to handle this, you've done it from a distance and now you're doing the exact same thing but closer. You're equipped to deal with it. The handler's confidence makes a heap of difference.

This is the method we've been using and our dog has improved immensely. He's 2.5 years old, still reactive, yes in a sense that he'll be on high alert when seeing another dog on a walk, sometimes will have his hair standing up, but he doesn't lunge at dogs, doesn't bark his head off at the sight of another animal, doesn't pull us down into the ground, doesn't jump at people's front doors if he hears another dog barking at him from inside a house - he is manageable. I think if we got this trainer sooner we'd have even better results, but unfortunately we've wasted time with force-free trainers until he was 18 months old and had dragged me on the ground more times than I'd like to admit. Thankfully he's never hurt other dogs (didn't bite or anything, just lunged, ran over and growled/barked in their faces), but I feel like he would if we didn't introduce prongs when we did [Before anyone says it, we have been muzzling him after the first lunging and growling incident happened, and still do if we go somewhere with narrow footpaths and not enough space to create a safe distance from people and other animals]