It's worth to notice that Marx never called it "Labor Theory of Value". Marx referred to it, and Orthodox Marxists still do, simply as "Law of Value". He seems to do no such arguments for what I've read on the net, so he might not be of any branch of socialism - at least not an existing one. Certainly not a Left-Communist or a Leninist/Trotskyist.
Apparently, he has the idea that much of 20th Century Marxism was a product of Engels. I don't know how he justifies that. Engels wasn't of the literary size of Marx, and he certainly did mistakes in attempting to publish Marx's works after the latter's death (dialectical materialism and state capitalism, lol), but to put blame on Engels for Stalin is kind of insane.