Going to keep this short; this is a very helpful product and teaches you great methods.
The only con would be that it doesnt offer much in the way of useful advice for prepping an entire campaig. This is due to the approach it presents requires much improvisation session to session making it impossible to prep an entire campaign.
i also would have liked to seen some sort of approach to quickly prepping dungeons.
There is a companion product that really should have been integrated within this as a single book. That product contains fillable sheets for the methods taught in this book, which is odd that they werent included here.
All in all if you want to run games with little planning on a session by session basis, this product is a great read.