I personally don't find metaphorical explanations helpful, especially considering this is not the only time I have heard or will be hearing about relativity, so if I get another explanation I will have to either map the concept of balls to whatever metaphor another teacher uses, which is just more work. I'm fine with using generic words like 'information', which I can map more naturally to other explanation wordings like 'signal'.

The same applies for explanations of bitcoin, or Machine Learning, or stock markets, just use the proper wording, difficulty, weights, secondary market. Metaphors are not teaching.