I've seen a lot of upvotes and downvotes on the content concerning furry, aeromorph and other anthro pics as well as commentary (on one at least).

IMO this isn't my fetish, neither planes nor futa, BUT does it fit the criteria of a leftybooru post? Yes, almost every single one.

prominent communist symbols? check

relation to communist countries? check

properly tagged and rated? check

lack of guro, vore etc.? check

For the planes in particular

As for quality, the pictures are high-res, most well drawn and content aside, are decent over-all.Compare this to the hundreds of ms-paint shitposts of stale memes, bad edits and other thread garbage that is far dumber, with 0 purpose.
If you don't like this content, get an account and black list certain tags for yourself.