I went on a paid trip to a Parelli three-day seminar in Pennsylvania with my 4-H chapter, as my 4-H leader was becoming utterly obsessed with their system. I was probably about 10 years old at the time, so 10 years ago. I had been taking lessons three days a week consistently since I was 4 years old with the same trainer, who encouraged me (especially since it was free) to go check it out for the hell of it. My instructor has always instilled in me that I should always look into new things, but there is no obligation to use them. That was the EXACT way I felt leaving the Parelli seminar. I was bored to tears during their demonstrations, while I did take some notes and agree with about 3% of the things that they were suggesting. But, at 10 years old, I could have told you how overpriced everything was and that it was a waste of money.
If you train with NH good for you, if you don't - good for you, and if you use a combination - guess what! Good for you! It is all about what works for you and what works for the horse, but this is also totally subjective as it really depends on where your skills are, as well as the horse's. I agree with everyone else, you bought into it for so long, you can't be mad at them for openly taking your money.
Be dominant, not violent. Be assertive, not aggressive. Take in all the information you can get your hands on, but only give out what works, what is true, and/or what is genuinely useful - and only when asked.