I needed to read a short biography of Huey Long before I tackle All the King's Men and this satisfied the "short" part. I got the basic facts. Though it is cataloged as an adult book, the language makes me think it's for middle schoolers. All the facts are there, but not much analysis.
Interestingly, though, there were a lot of resemblances to the Lyndon Johnson biographies in this book, particularly in describing the poverty of the South in the early 20th century and the ruthless (lying) campaigning. Caro's book helped me understand a bit about Louisiana.
This book gave a good overview of this controversial figure. It was just what I was looking for in that it was short and easy-to-read while also giving me a look into what my state, Louisiana, was like during the depression.