Parelli's products are incredibly expensive and some of them are silly. I honestly don't think a carrot stick and progress string is necessary but it has worked well with desensitizing my horse to having things throw in his direction and touching him as I toss the string over his body. It also helped cure his ear/head shyness as well as helping him be okay with ropes twirling around his legs so that way if his foot gets caught he won't panic.
I like John Lyons too as well as Monty Roberts. I do what works for me.
I make my own parelli gear, I order quarter inch yacht rope online and tie my own halters and make my own yacht rope leads since I recently learned how to properly make an eyesplice and backsplice a popper in place. I bought a fiberglass rod from a Parelli off brand company and attached my own savvy string for twenty bucks total versus the prices he charges and the products work the same.