Fifty years later, this is still a first rate source and still a fairly excellent book to learn about pre-independence Rwanda and Burundi. This could even be the first book you read on Rwanda and Burundi, it really gives you an excellent grounding and you could read almost any other book on pre 1960 Rwanda and Burundi after this
The negative sides are that there is still a small touch of Euro-centrism in his work, later experts like Desforges, Prunier and so on were less tainted with eurocentrism and a bit more interlacustrine focused.