Once you become confident enough in your own ideological convictions as a Marxist-Leninist there is no reason why you can't draw on sources with all sorts of different ideological inclinations as long as the analysis they provide is solid and valuable.

This is literally what Marx and Engels did. They read Smith, Ricardo, Malthus, etc and it was all important in forming their thought. They even read scientific stuff like Darwin, etc.

I think leftists need to look outside their little bubble otherwise things are going to blindside them. One example I can think of is how most lefists were completely blindsided by Andrew Tate and didn't even know about him until after he had already blew up and was on the verge of having all his social media purged. And the standard response is "hurr durr why do I need to know about him, hE's A nObOdY!!" I mean yeah, to you he might be but he was super influential to millions of men and boys(and still is). And if you want to reach these guys you need to know what they are immersed in. Then you can apply a mass line tactic of sorting them into advanced, intermediate, backwards and do all that analysis. But you can't analyze what you aren't even aware of.