Haven't read that one, but I did enjoy Byron Farwell's biography of him. I'm currently (slowly, when I get a minute here and there) reading William Harrison's "Burton and Speke," the novel that the Mountains of the Moon picture was based on.
Must say I'm really enjoying it. Really brings the two men to life, notably Burton's obsession with sex, and Speke's growing exasperation, envy and distrust of him. You also get a real feeling for just how unpleasant and squalid it could be trekking through the uncharted wilds of Africa.