Like many of the postwar writings of ex-Confederate officers, Mosby's memoirs are, at some level, agenda-driven and self-serving. In his case, it was designed in part to sanitize the legacy of Stuart.
Most military historians are critical of Stuart's actions in the Gettysburg campaign, and nothing in Mosby's memoirs have prompted a need for a revision of the history of that campaign. Not only did Mosby play no part in the campaign, he was not professionally qualified to render an opinion on the subject. Mosby was a partisan ranger who never commanded more than a couple of hundred men in his irregular cavalry force. He had little or no experience with the combined-arms tenets (cavalry supporting infantry) of large military formations. He was very, very good at his job (one of the most effective "special operations" commanders of the war) and had an impact on Union army operations far out of proportion to his small force. But an officer skilled in the traditional role of cavalry he was not, and therefore has nothing authoritative to contribute to a discussion of Stuart's role in the Gettysburg campaign.
Those reading Mosby for the first time might want to know that Mosby was highly unpopular throughout the South after the war, due to the fact that he cozied up to the Republican party soon after the war, got involved with Reconstruction politics, supported Grant's presidential campaign, and was rewarded with a patronage post as U.S. Consul in Hong Kong. It is believed by some that his memoirs were at least partly an attempt to re-establish his Confederate credentials.
Generations of military historians have studied the Gettysburg campaign from every conceivable angle, using all available records, and the history of the campaign is pretty well decided on the role of Stuart. Mosby's memoirs have been studied, cited and given due consideration. The memoirs have not made the case for revisionism.