Orwell's unit was almost all anarchists.

Also, Orwell served in POUM's militia, not with the anarchists.

The unit's members, not its flag, hence "almost all", which would make no sense describing the unit's affiliation.

It is necessary to explain that when one speaks of the P.S.U.C. 'line' one really means the Communist Party 'line'. The P.S.U.C. (Partido Socialista Unificado de Cataluña) was the Socialist Party of Catalonia; it had been formed at the beginning of the war by the fusion of various Marxist parties, including the Catalan Communist Party, but it was now entirely under Communist control and was affiliated to the Third International...Roughly speaking, the P.S.U.C. was the political organ of the U.G.T. (Union General de Trabajadores), the Socialist trade unions.

...

In any case the loose term 'Anarchists' is used to cover a multitude of people of very varying opinions. The huge block of unions making up the C.N.T. (Confederacion Nacional de Trabajadores), with round about two million members in all, had for its political organ the F.A.I. (Federacion Anarquista Iberica), an actual Anarchist organization.

...

The P.O.U.M. militiamen were mostly C.N.T. members, but the actual party-members generally belonged to the U.G.T.

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In Barcelona there had been a series of more or less unofficial brawls in the working-class suburbs. C.N.T. and U.G.T. members had been murdering one another for some time past; on several occasions the murders were followed by huge, provocative funerals which were quite deliberately intended to stir up political hatred.

Those are from Homage to Catalonia.

I include the anarchists (CNT) and the Catalonian independent Marxists (POUM) among the "small-c communists." We can quibble about this designation, but I think it's fair...I'm also sure that members of POUM would not have had any problem with this label, being self-proclaimed orthodox Leninists.

The minority U.G.T. Leninists wouldn't, but the Catalan draftees who were members of anarchist unions (which were strongest in Catalonia) would.

it is indisputable that the parties for which Orwell fought were...violently intolerant of any opposition

If they were so violent, they wouldn't have let the Communist minority grow in power until they killed them. They were really violently intolerant of some opposition, which is not the same quality of thing, for many are violently intolerant of some opposition, the extreme stances being violent intolerance to no opposition or all opposition.

The analysis at the first link is pretty decent factually, and not a flat caricature either. I don't completely agree, but the objective picture feels correct. Indeed, when reading Homage to Catalonia, it felt obvious to me that Orwell was mostly charmed by the contrast between his comrades in arms' heartfelt quasi-religious attitude and the emotionally stunted life of Western middle class. He was conscious that they were in essense a barbarian tribe crossed with a Puritan sect - seeing all out-groups as not quite human unless proven otherwise - but chose not to apply all the boring ethical standards to them. Even later in his life he showed a certain insensitivity to slaughter of "innocents", coldly pointing out that there shouldn't be an ethical difference between soldiers & civillians. Indeed, he was a little bit of a fascist, although closer to Nazism than to Stalinism in his darker moments.

However, calling the Spanish Anarchist rule "totalitarian" is pointless abuse of the term, of which I prefer Arendt's strict and horrifying definition. (See her work Origins of Totalitarianism.) It was, in essense, the rebirth of some scavenger values, painted red mostly for political utility and planting a few Marxist ideas into rich soil. And they certainly were the heroes of their own stories - it's moral myopia and not everyday heartlessness that appears to be their cardinal sin.

I'm not especially a fan of anarcho-syndicalism, as you can see. Even in theory it can threaten to throw out civilization's baby along with the bathwater. And even disregarding the out-group interactions (which are psychologically imperilled whenever in-group consciousness strengthens), it depends too much on morale, high spirits and good leadership.

Which is also my answer to Eugine_Nier's criticism of Alinsky's work - his approach to everything was heavily Syndicalist (not Socialist), he was proud and stiff-necked and it could've rubbed off on the black communities he sought to unite; without guidance, their new-found voice and political power might've served to plaster over long-standing internal problems and reduce the relative attractiveness of self-improvement in blacks' eyes (the material incentive for "breaking out of the hood" shrank as life got better, but it's a tall order to cultivate ideological and cultural incentives during a short window of a community's eagerness to change).
Yet I feel certain that doing nothing for those benighted, long-suffering people was morally unacceptable. And I haven't heard any better counter-factual proposals from anywhere right of center - it's just "Segregation was not so bad, leftists are whining over good old ways, equality of outcome is horrible anyway" from what I've seen of their criticisms.

(I'm not going to read the second link, as I've had enough of Comrade Sam for the next few centuries.)

Edit: oh, the author is an Anarchist himself, and looks fairly broad-minded too. I was afraid he's got an orthodox libertarian bottom line, given who linked to him.