The Idea is a history of anarchist communism. Communism as in ‘from each according to their abilities, to each according to their needs’ which appeared in various forms in the working class movement as socialism and then anarchism evolved after the French Revolution (and long before the word was used for the ‘jam tomorrow’ of the post-1917 Russian ruling elite). So, anarchists who see no role for wages after the revolution are communists (‘to each according to their productivity’ is for collectivists). But it’s a bit more complex than that, as anarchist communism (more tightly defined) represents a strand distinct from syndicalism and anarcho-syndicalism (though as you’ll see the FORA union of Argentina was – most of the while – anarchist communist; and anarchist communism and anarcho-syndicalism in 1930s Spain were interpenetrated ). There’s also the question of how to organise and what tactics to follow.
Heath is a partisan of organised anarchist communism – and has no problem with ‘struggle, contradiction and acute dissensions’ . For example, he warns against the ‘yellow fever of individualism’  and ‘virus of spontaneism’ . His verdicts are clear and, thankfully, he doesn’t twist the facts to bolster them (he doesn’t share Luigi Galleani’s anti-organisational approach, but doesn’t try to deny his anarchist communism ). It’s sad to read of so many who saw the value of organisation, yet ended up leaving the anarchist movement ‘behind’ for groups that were definitely very organised but not much use at liberating anyone (Maoism, Trotskyism).
Heath has written a huge number of biographies of anarchist militants, (see https://libcom.org/tags/nick-heath) a huge effort of ‘history from below’ that you might think would be enough work for one lifetime. The Idea does not compile them, it’s a separate project; but it does have some of that wonderful sense of letting past comrades speak, and showing their anarchist communism in context. Here’s Erich Muhsam in Germany: ‘We claim: no one can be free as long as everyone is not free.’  Or Li Shizeng in Paris, rejecting Daoist ideas ‘Anarchism advocates radical activism. It is the diametrical opposition of quietist nonaction. Anarchism does not only advocate that imperial power does not reach the self; it also seeks to make sure that it does not reach anyone else.’ 
It’s a shame there’s no index, though I can see why the publisher thought the extra pages might be too much. I would have liked fuller references (some chapters have them, some not) but I doubt that will stop anyone hunting things down.
I think the parts of The Idea based on personal experience will be a useful source for other histories of anarchism. But mainly The Idea is a full (and honest) history of anarchist communism: ‘The history of anarchist communism has been full of many defeats, of scissions and failures. Yet it has perennially renewed itself, attempting to learn from the mistakes of the past.’  It’s an epic achievement.
The Idea by Nick Heath. Published by Just Books Publishing, 2022. ISBN 9781739723712 https://organiseanarchistsireland.com/product/nick-heath-the-idea-anarchist-communism-past-present-and-future-copy/