There are some books that I read that I think everyone should read and there are others, that are probably only for a specialist readership. Christian Mission in the Twentieth Century almost certainly falls into the latter category.
That doesn’t mean it isn’t a good book; in fact it’s an excellent book. However, with the best will in the world, it covers a narrow field which will not interest everyone. If you are interested in the development of missiology in the twentieth century and things like the 1910 Edinburgh Conference and the development of the International Mission Council, the World Council of Churches and Lausanne are you thing, then you should buy this book (though you will probably have read it already). If not, grab a copy of The Penguin History of the Church: A History of Christian Missions: A History of Christian Missions v. 6 (Hist of the Church) by Stephen Neill and get a much broader perspective.