This is a critical, moralizing, incomplete and incorrect biography, the latter owing to the fact that the greater part of Boswell's papers was either unknown to Vulliamy or had not been read by him. The famous London Journal had not yet been made public at the time, hence Vulliamy's writing that "[i]t is impossible to follow in detail the course of his life between the end of 1762, and his meeting with Johnson on the 16th of May 1763". Actually, that exact period of time is today, one of the best documented periods of Boswell's life.
Vulliamy is extremely critical of some of Boswell's acquaintances as well, especially the unpleasant group, to whom he was introduced on May 24, 1763, at Bonnell Thornton's. John Wilkes is described as "one of the worst and most amusing men of his age [...] presid[ing] over the tavern revels of those who were classically indecent and wittily blasphemous." Charles Churchill was "the most profligate rogue who ever wore the dress of a clergyman, who died at Boulougne in 1764, burnt out by all the disorders of a vicious life." Robert Lloyd "fortunately extinguished himself when he was thirty-one, ruined by his friendship with Churchill."
With this in mind, it isn't difficult to imagine what Vulliamy thought about Boswell's going to prostitutes and drinking with Johnson and others.
The book has some historical value and offers a somewhat (unintended) entertaining view of Boswell, but Vulliamy didn't have as much information available as we do today, and so the book isn't in any way to be deemed a reliable source for information about Boswell's life.
James Boswell by C. E. Vulliamy was first published in 1932 by Geoffrey Bles, Pall Mall, London.