I'd stick with flexbox, it's the best choice for now. Using absolute positioning can introduce more bad things, than good.
Here's a neat little game, which can teach you flexbox in no time.
Yes I agree, but this is meant for situations where flexbox doesn't work, it's pretty rare but it happens. This method is more of a last resort than "use this intstead of flexbox and automatic margins". I'll add a little note to the post.
EDIT : It's particularly useful for centered absolute pseudo elements.
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