Are Vertex's balls actually that big? Or is that just like, some type of magic potion or something?

It’s kind of both. They’re not naturally that big, but it’s permanent.

However, Vertex does have and enchanted tail ring that shrinks stuff down to a more manageable level in case he needs to go somewhere or something.  The tail ring only changes the size, so the weight and cum production still remain. I’ll elaborate more on that in the future.