As an overview of Twain's life, this bio was nothing more than "ok". It goes into little detail on the major events of his life, yet wants to dwell on the trivial. It does little to add new light to Twain's writings.
It tries to make up for a lack of substance by speculating on Twain's sexuality. The author speculates that Twain probably engaged in homosexual activity following this logic:
Miners were lonely
Miners did not have women for sexual company
Miners turned to each other on occasion
Twain was a miner and knew lots of miners
Twain therefore turned to other miners for sex
And
Some of the writers and artists in San Francisco were homosexual
Twain was a writer in San Francisco
Twain knew other writers in San Francisco
Twain was homosexual
It is hardly a convincing arguement and ultimately seems to be thrown in more for titillation that for any meaningful reason. There are much better bios of Twain to turn to.