Is it worth the read? I recommend Tunney: Boxing's Brainiest Champ and His Upset of the Great Jack Dempsey. It's a great book and from what I learned about Greb from it, I am utterly fascinated by the man. Beat Tunney as a middleweight if I call correctly. Man was a beast and fought with one eye for a while!
I've read this biography of Gene Tunney, which also contains a fair bit on Jack Dempsey and of course, Cinderella Man.
Personally, books about the good old days of boxing interest me far more than any of the modern stuff you see written. It's amazing to see the amount of respect the sport had back then and how boxers were the celebrities of their day. Anyways, I read Cinderella Man first and then Tunney's bio, but if I had to do it again I'd start with Tunney's story because it'll give you a good background on a lot of the fighters mentioned in Cinderella Man.