Oh my goodness, so many responses. Not going to bother responding to everyone. I said what I said and stand by it, a bunch of entitled opinions here that are upset about things that they would have no idea or clue about if done properly.
Why are player's entitled to know everything? Player's being told what was and was not modified in their adventure is such a meta thing to do. There are a lot of things that need to be hidden from the players, and if an invisible railroad is used the way the author intends then player's will not...
This is a great article and I'm surprised how many are commenting that they don't like this idea. I mean, what's next? Will you be upset when you learn your DM just made up everything?
"[contains] the demon lords from Out of the Abyss," Perhaps I am incorrect, but I believe these monsters are all in the Tome of Foes (as well as Zariel and devils from Descent into Avernus)
This review inspired me to check out this book and the website. I decided to buy the book, and wow is it pretty great! I can't say I've gone through and read the 500+ pages yet, but the quality of everything has been great so far