I think the prong will give you a much better means of communicating with your dog - so it should be a better tool for what you're dealing with than the gentle leader.
I'm glad you'll use it guidance from a trainer, though, since you want it to be a positive association for the dog and not just a means of punishment.
With our last dog, we used - at different times in his life - a flat collar, a nylon slip (show) collar (basically a quiet choker), a gentle leader and a prong.
He was a pretty easy dog (for us) to handle, but he would get over-excited with our dog-walker. She didn't like using the prong, so she used the gentle leader. The dog didn't like the gentle leader, but he was more interested in the walk, so didn't let the collar stop him (it did, however, calm him down significantly).
He had no problems with the prong, but I agree - they LOOK scary (and make the dog look "mean") - so we normally opted for the slip collar. He could back out of a flat collar, but otherwise he would respond well to that for us, too.
Our bulldog rescue... who was a bully when we first brought him home did not respond at all on a flat collar, and I was concerned of strangling him with a slip or choker of any sort... so we went with a prong. BEST thing ever! We used a puppy prong with him - smaller links, with soft tips (you can also get plastic covers for the tips to make them even softer than the filed metal ones... but AVOID cheap versions - non-filed tips can be SHARP). As soon as that prong was on him, he would go from a '9' to a '5' on the 'deaf bully' scale, so we could get through to him and redirect as needed.
Prongs are great tools - but they can be dangerous if used improperly. One of the worst stories out on the interwebs is of a big dog tied up on his prong... he went after a squirrel (or some small animal) - got a good 20ft head start... hit the end of his rope and impaled his neck on the prong - he survived, but the initial pictures were not pretty. The owner in the story was VERY sorry... But, just a nasty reminder, the prong is for TRAINING, not for casual tie-out, and really, should not be left on the dog when you're not on the other end of the leash. Note - if that dog had been chained on a choker, he probably would not have survived...
One of the best videos I saw of introducing the prong was from Tyler Muto on YouTube - if you google "YouTube Tyler Muto Prong" it should pop right up.
The other side.... I tried putting a prong on Denna, just to see how she'd do, and if she'd respond well to it... NOPE. I put it on her when we were 1 block from the house on a causal walk... just putting it on, no pressure AT ALL - she flopped to the ground and wouldn't move. She'd let me drag her home with it (which I obviously didn't do), but she was NOT moving with that on her neck. She's a sensitive girl! As soon as we went back to her slip collar, she POPPED up and we were out on our happy walk again. Silly dog!