I bought the Juggernaut 2.0 ebook, it was okay. I don’t have the original book, but the variations in the book aren’t anything very different from the original program.
The inverted variation is just the sets and reps from the 10s and 8s phases reversed. So instead of 5 sets of 10, it is 10 sets of 5. The undulating periodization model switches up the order of the phases like this:
10s
5s
8s
3s
If I were to run the program that is how I would do it. That way you don’t go 3 months without handling meaningful weights.
Even though there isn’t much in terms of variations on the program, there is a ton of knowledge in the book that is worth reading. Smith really knows his stuff about training athletes and I definitely learned some new stuff. I don’t know how much of that is new stuff though, since I don’t have the first book.