The last chapters, dealing with Newman as a person, were by far the most interesting and enjoyable for me. The earlier chapters, tracking his theological progression from nothing (ish), to evangelicalism, to Anglicanism, and ultimately to Catholicism, could have been interesting but I found them pretty dense and dry. They assumed a lot of prior knowledge about the Early Church Fathers, schools of theological thought and of heresies, other prominent theologians, etc. I suppose it's what you would call 'scholarly' - it's very heavily referenced - but that wasn't really what I was after in a so-called 'Very Brief Introduction'.
All that said, it painted a good picture of Newman, his thought, his person, and his significant contribution to theology. It was a good illustration of the fact that sainthood is not the same as 'being a good/nice person'. Newman was, Duffy says, rather self-absorbed, over-sensitive, inclined to hold grudges, and at times quite unkind. However, he was radically committed to seeking truth, willing to express unpopular and unorthodox opinions, and therefore poised to contribute some of the most original and revolutionary thought/theology in Church history.
Having read this, I feel better able to turn to Apologia Pro Vita Sua, Essay on the Development of Doctrine, and the Grammar of Assent, with some context in which to understand them.