First up, awesome, awesome product! My son used it at school and with his birthday coming up knew exactly what he wanted. He loves it.
I think a worthwhile edition would be some sort of brake to stop the machine from starting before the user it ready would be a great addition. Something as simple as some pins on a tab that can go underneath the bottom levers would be more than enough. It can be a bit frustrating if you accidently trip the machine when loading balls, more so when a younger sibling is helping!
Otherwise, wonderful product.