First half of the book was adventures of Durruti robbing banks around the world. Highly entertaining but not that much substance, would recommend this to any 9-12 year old.
Second half had more interesting stuff. Attempts of syndicalists to raise uprising in Rif of Spanish Marocco in 1936 were interesting, although eventually sabotaged by social-democrats. This is a solid proof, that anarchists of the golden era took anti-colonialism seriously, and were open to an idea of a common front with islamists against fascism, in contrary to what people like Fredy Perlman or Bookchin would claim later.
Another interesting aspect, especially from a Nordic point of view, was relationship of Durruti with social democracy. Durruti, just as Rudolf Rocker, apparently considered that there was just a narrow time frame for anarchists to depart for a radical alternative, before social democracy would take a persistent hold of the labour movement. They were right, but this is also a sort of contradiction with view of some classical anarchist (such as Bakunin) that there is no need of "right material conditions" for creating anarchist alternatives, view which is popular today amongst insurrectionalists.
My main reason to read the book was that I was interested about Durruti's position on materialism. This was not cleared much, and in the end I believe that FAI never had very clear analysis what in their practice is different from Blanquism of Bolsheviks in 1917. Ok, there is a promise that there would not be terror or repression of peasants, but still it is about a vanguard organisation. FAI was not very consistent on prefiguration.
Durruti had a clear understanding that he was a charismatic leader with a huge responsability and exceptional capability, but should anarchism be about replacing bureaucratic authority with charismatic authority? Durruti had almost no flaws, he was even a sort of feminist of that time, as there was a period when he was basically a housewife taking care of a baby when he was blacklisted by employers, for which he was ridiculed by some more traditional comrades... but when all the most charismatic leaders are shot, what would FAI do?
To be honest, this book made me more interested about trentistas of Pestana and their criticism of Blanquism of FAI, and less interested about FAI, although FAI was way more solid on anti-colonialism than Pestana. It is obvious, that vast majority of FAI considered their insurrectionary practice a failure by 1936, and this is why they made choices which have been criticised since then.