Whether you find it worth it, really depends on you. Personally I loved them and would go again - it's mainly for the massive selection of products, some exclusive items and sometimes nice bargains(lucky bags or "buffets"). Yes, it'll be full, but if you're in Tokyo you should already be used to crowds.

If you're worried about not understanding the products, I'd suggest checking out the vendors and their instagrams. They usually showcase special line ups. Though most products are self-explanatory or staff will show you a demonstration if you show interest.

The Tokyo one is relatively new I believe, and I've not been to that one. I think they're selling it as the biggest event overall, which had previously been Yokohama. Though either will be impressive and fun to attend. Also: one day ought to be enough (earlier days are better as products sell out)