At least for some people, or as a second read after the official Rust tutorial book.
I just read the first 7 chapters of the shipped PDF version, and I think it is quite useful for refreshing my memory. The first 10 pages are a bit weak, so when I discovered that book first two years ago, I stopped reading it early. But the later chapters are quite nice, it is a compact repetition of the most important Rust concepts. There are a few typos, and not all explanations are fully correct. And the book might not cover all details. But the authors English is quite good, and he explains the stuff in his own words, sometimes comparing Rust concepts with Java, JavaScript and Go. I assume that the book is still better than most books sold at Amazon, so it is a bit sad that it is so difficult to discover this free book. It was announced in Feedback Requested: The Rust Book Abridged, and it is still hosted at The Rust Book (Abridged) | The rs Book