An older book, written with old sources - the Marx-Engels Werke rather than the Marx-Engels Gesamtausgabe in its current much more complete text. It therefore misses important details present in the careful scholarly work of recent intellectual biographers of Marx - Sven-Eric Liedman & Michael Heinrich. Yet Manale & Rubel present a coherent picture of Marx in his intellectual life, political activity and personal trials, whereas Liedman's is so solely an intellectual biography that he manages to obscure the person of Marx developing the ideas. (Only one of Heinrich's projected 4 volumes is released, so comparison is currently impossible). This book does manage to provide a view of Marx much more realistic than the sainting & demonizing Cold War legends that still surround him.
The reason why this book is interesting is because it really seems that the Russian Marxist and communist Maximilien Rubel (and co-author Margaret Manala) are honest about Marx, Engels and the revolutionary movements that grew up in Europe from around 1848 onward. This makes us see Marx's good nature - he cared about his family and friends, outraged by the abuse of the state of 'the upper class'. And his bad nature (easy to irritate, often temperamental, narcissistic, violent in his thinking (revolutions), borderline delusions of grandeur, and severe lack of understanding of the scientific method. The latter is understandable given he grew up and was educated in Germany, heavily influenced by the nonsensical Hegel, with his obscure dialectics and belief in 'laws of history'. Marx never escaped Hegel's 'method' - becoming a 'materialist' did not help him, and never escaped his 'historicist method'. The palpable psychological quality of both Marx of Engels was their fierce need to 'critique' almost everything they read, giving the impression that they believed 'only we know the truth'.