The POUM were Trotskyists and most definitely did not have "anarchist leanings". The only commonality they had with the anarchists (who were far more numerous and militarily effective) was that the Communists attacked both of them.
Not exactly Trotskyist either: Andres Nin the leader of POUM had his differences with Trotsky and they did not have contact after 1935 - so it was something like an independent Communist party.
POUM had its differences with Moscow controlled Communists (the third International) - Moscow was for a broad coalition government that would postpone socialist reforms (that's called the 'Popular Front' approach, similar to what was done in France); while POUM was all for pressing on with socialist reforms right during the civil war (mostly within Catalonia). So POUM was more similar to the anarchists in its politics, but the anarchists were much larger movement than the Marxist POUM.
In any event POUM was a small local party that did not matter a lot, but its suppression (that went on with the persecution of the Anarchists) in later stages opened rifts within the Spanish Republic. All that happened once the Spanish government came under increasing control of Moscow - that came as a result of international isolation while the Soviet Union remained as the only backer.
Left wing politics is all very factional, so it gets complicated. I think the Popular Front approach would have been more productive, but Orwell for example did not think so; in any event it became quite bad once the NKVD came in.
Having said that I fully concur with your recommendation of Homage to Catalonia. Amazing book about a pretty amazing time.