Hi Philippa,
in the foreward, the author states,
"This book portrays the lives of 88 convicts transported to Van Diemens Land, New South Wales and Western Australia.'The Michael O'Brien mentioned in the book was born in 1826, one of five children to John and Mary O'Brien in Dublin.
He was arrested in 1843, (in London) and arrived in Hobart in Oct 1843.
He married Margaret McLean in 1855, Hobart Town.
Going by these date, sadly I cannot see a link with your Michael O'Brien.

good luck with your search.
Margaret