This is a good one.
I'm picky and choosy when it comes to Estleman--that says as much about me than it does about him (I'm not a mystery buff; many of his books are mysteries; nor am I a western obsessive; if he wrote nothing else he'd be a success.)
However, when he writes something I'm interested in I REALLY like it. This is one. A nice blend of factual (not just the character, but the period-piece detail of time and place; prohibition Florida) and fictional story. I'm writing this about three years AFTER I read this book, and that also tells you something--certain scenes and the ambiance of the novel itself stick with you. That's very good writing.
For the best, in my opinion, read Estleman's The Master Executioner. One of the best books I've EVER read. And a western, too.