Historians are generally hesitant to call books by laypeople "good history." I haven't read this book, but it's probably a great way to understand Churchill, especially if you read it alongside some scholarship on him. That said, if you find it interesting, read it! He certainly put a great deal of effort into the, what, four volumes? And he was intelligent, educated, and invested in the story he was telling. That being said, I would probably find it a bit boring.

If you're interested in the historical period Churchill is writing about, you might check out this book. It's written by a historian, but it's intended to be pretty accessible to non-professionals. You should be able to follow citations to less-general work on the period if something catches your interest.