Disclosure: I received this product for free. (Though as you'll see by the end of this review, I'd have gladly purchased it once I saw what was in it.)
One of the greatest challenges of using a new system like Level Up, even when it has the amount of backwards compatibility that Level Up does, is that by definition a new system with just the core books can't cover everything you might want to convert from an existing campaign or setting.
In the case of Level Up, that's pretty easy with classes and subclasses; you either have a new version (class) or it's fully backwards-compatible with the old material (subclass) and you can just get on with it.
But the part of character creation referred to as "origins" by the Level Up rules is a greater challenge. While the Adventurer's Guide covers a lot of popular options like humans, elves, gnomes, orcs, dragonborn, and so on, if you've been playing something more unusual, it's a bit harder to move a character over.
And this isn't even mentioning the homebrewed or adapted campaign setting with entirely new heritages and cultures in it that you may want to run or play in. What to do?
Well, this product provides the resources to quickly and easily fill those gaps without a lot of fuss over balance or creator's block getting in the way.
The book is divided into three main sections, each covering one of the three main components of a character's origin. Each opens with an explanation of what this particular component of the character's origin represents.
The first is the heritage section, which contains a dizzying number of new options for biological abilities of whatever new species you're looking to play. They are set up in an easy-to-use point buy format, and the authors even helpfully provided a form to plug them into in the appendices, so when you're done you have your new heritage in a useful form rather than just a loose collection of notes. Those familiar with the popular Detect Balance tool online will find this familiar, but rather than using the book to determine whether something is balanced, you can use it to build something you know won't bite you in play.
The culture section follows broadly the same structure, providing a point buy framework to construct cultures with. I suspect that for serious world builders, this will actually see more use than the heritage section, as unique cultures are an important part of any fantasy world. As with the heritages, there is a form included in the appendices to fill out as you construct your new culture.
The background section is the smallest of the three, which is appropriate because backgrounds tend to be the least fiddly in terms of mechanics, but even here the book provides an alternate take on ability score adjustments and some useful guidance and three pre-made ones that can be dropped into most worlds with little fuss.
I would also be remiss if I didn't give at least a nod to the writing style of this book. This is the sort of project that could be forgiven quite easily for being dry and bland, but it manages not to be. There are some great moments of genuine wit and humor, a few fun pop culture references, and a pleasant, conversational tone on offer here alongside the highly-functional mechanical material.
Finally, it should be noted that the lead author of this book was part of the initial Level Up design team, so concerns about whether the author actually understands the system should be moot; this was written by someone whose name appears in the credits of both the Adventurer's Guide and Trials and Treasure.
All in all, an excellent, highly-functional product that I will be using in my own games.