It won’t. What it will do is allow successful revolutions to have a large trade partner to help develop their country. But China isn’t in the business of spreading revolution or defending allies like the USSR was. If Cuba got invaded by the US tomorrow I highly doubt China would do much more than try and coordinate with the UN to stop it or something. Perhaps they may secretly fund Cuba or whatever but again, I doubt anything directly. Not hating on China or anything. Its perfectly reasonable to look out for yourself first as a country. Even if it seems a bit, nationalist (because it is), its a reasonable approach.
Better than nothing. Like any org, local chapter is the most important thing. There are green party chapters with MLs in charge and there are PSL chapters with sex pests in charge. Try and see what they do in your community. If they do work you agree with, great, if they are inactive or you don’t like the work they do, find something better. Can’t hurt to check it out though. Maybe great, maybe terrible, but you’ll never know if you don’t show up and see for yourself.