There are different lines in different breeds. Just because some spaniels can take certain things doesn't mean your spaniel will.
Gentle leaders/haltis are not meant to be used for corrections. Instead of jerking him and potentially hurting him, can you just stop and call him back to position and as soon as he is back in position, start moving forward again? I hate pinch collars, but I'd rather see a person walking with one correctly than jerking a dog with a halti or gentle leader. You should be training him in the house, then the yard, then on walks. Slowly and helping him be right. You don't just take them out and punish them for doing something wrong that they don't even know is wrong to begin with. It's really not fair to dogs or even humans.
I'd also be nervous about the entering and greeting thing. The dog is sketchy with people and having someone come into your house, yell at your dog and walk into him yelling at him is not going to help. I'd just manage my dog versus doing this if I had to, which I do because I don't have company enough to worry about it or practice. I mostly meet friends out in public places. Can you crate the dog with a bone when people are over and let him out once he's calm, on a leash, helping him sit for pets or something?
OMG...+R training is NOT 100% positive. Most dogs do not find being denied of their reinforcer to be positive! A reinforcer is walking forward, going to sniff something, getting food, retrieving something, going in/out a door, going in/out of a car, etc. You teach them that they can have or do whatever for whatever it is you ask. It's showing the dog what you want and helping him be right vs. not showing the dog what you want and then punishing him when he's wrong.
The online classes are not for everyone. But they are interactive and super informative. They watch videos of you and point out exactly what you are doing right and wrong at the exact time on the video. Sometimes they do screen shots and circle things. Sometimes they video themselves doing something for you as an example. There are cats learning how to retrieve and hold items from these online classes. People are getting very high level titles in a variety of dog sports from the online classes, some are even from other countries and English is their second language. There are people with mental and physical disabilities learning from them, even, as well as children. These instructors are the best of the best and very well-versed in how to teach online. They provide a ton of attention. So basically, you spend about an hour a day with them about five days per week. Again, you have to be committed and serious about the work you're willing to put in because it is like a college course with lectures, practicing, communicating with classmates and your instructor, etc.
If you chatter nonstop your dog won't listen when you do have something to say. They'll tune you out. Also, your dog shouldn't have to worry about your mood; it's not his problem. You can't be emotional when you train your dog because you can't be consistent.