TL:DR = THUMBS UP!
First of all, I love the cover! It evokes the spirit of solo roleplaying. I'm a semi-experienced solo rpger and have been hanging out on the Solo Roleplaying subReddit and Discord for a while now that's run by the author. I encourage you to check it out, we are a welcoming and helpful bunch!
As part of that experience, I've learned a lot about solo rpging and didn't know how much I would learn from this supplement. I was pleasantly surprised! As the title indicates, the product starts from the ground up and explains the basics of what solo roleplaying is and how to do it at a basic level. This filled some gaps in my knowledge. As a semi-experienced solo player, I was also looking for additional insight and wisdom. Alex provides this through sample scenarios and elaboration of how the techniques are used in play. The nice thing is that he presents it all in a conversational tone without interjecting his personal preferences. There's solo philosophy in here! At the end he provides links to the subReddit, Discord, and some recommended starting solo resources.
There are only a couple of very minor caveats. The first is that it is usually assumed that people who decide to get into solo roleplaying are at least minimally experienced with at least one RPG. This is just how the progression generally goes. As such, Alex doesn't explain the basics of what an RPG is, but starts from that baseline and explains solo from the ground up. That doesn't mean you couldn't read up on RPG's first, then take on this book afterward. Secondly, while he gives examples, I'm sure some will want more. My impression is that Alex was staying true to the word "brief" in the title and that was one of the reasons for including the subReddit and Discord.
As an aside, this product is an introduction and his other product, Tilt, is an evolution of two more advanced techniques and advice. It is excellent as well!