Yes I know, I have his book The Severans: The Roman Empire Transformed. But this book and I think The Antonines too are only the hybrid of his two books - History of Rome, The Roman Emperors: A Biographical Guide to the Rulers of Imperial Rome. It´s true that you find a little more information in books about Severans and Antonines, but most info you will find in the two books I mentioned (I found it very repetitive in The Severans, it´s a waste of my limited financial resource for books to buy The Antonines and there are several Pen and Sword books and two Osprey upcoming ). But his other books are great, like the Cleopatra´s biography and The Fall of Roman Empire.
Still I like Michael Grant´s work.