I enjoyed reading the content but gave it 3 stars because of the price. I peronally don't like reading PDFs so needed to print it out. My biggest criticism would be that the sample picture of the Index page is great - however the paragraph "Campaign Logs (page 24)" doesn't correspond with any chapter of the same name in the index.
The product is worth buying, and perhaps it's me, but I don't understand why the author hasn't created a supplementary video to show highlights of the book. I'd pay extra to view the video. The author does mention that there are ample bullet journal videos on youtube, but not specifally for gamemasters. Overall this is a good product, I just don't fully undersand the instructions.
I tried finding the contact info of the author to send a friendly suggestion email, but was unable to find the contact info.