The Brahmo Samaj and the shaping of the modern Indian mind By David Kopf
For people seriously interested in a Westerner's perspective on Brahmoism's development, this entertaining (if sometimes wildly inaccurate) book is available online couresy google. (A limited preview).
As the author acknowledges at the end, his book was mainly based on the Sophia Dobsot Collet section of the Sadharan Brahmo Samaj library (and grew out of his attendance of the Sammilan Samaj's Brahmo Conference at Hazaribagh in 1971).
Kopf also concludes (in 1979) that Brahmoism's biggest enemy would be Marxism.
http://books.google.co.in/books?id=IUcY_IRKDHQCThe Brahmo Samaj and the shaping of the modern Indian mind
By David Kopf
Edition: illustrated
Published by Atlantic Publishers & Distri, 1979
ISBN 0691031258, 9780691031255
399 pages