Betaine HCl is supposed to support your stomach if it’s not producing enough acid. Supplementing enzymes supports your pancreas. I guess if your stomach was struggling, your pancreas would be too, so that’s probably why a lot of supplements combine them.
Able highly recommends bitters, and there’s some research that suggests they’re effective. They encourage your body to produce enzymes, whereas tablets are a straight supplement that won’t necessarily help your pancreas learn to do what it should.
People say HCl encourages your stomach to naturally produce more acid, so that you can stop using it eventually. As far as I’m aware, there’s no research to confirm or debunk it, so I guess you just have to try it out. There’s a lot of anecdotal evidence of success. Make sure you get it combined with pepsin.