I know this is not a new problem, but I still remind as it's a very basic logic.
Why can't customer choose quantity for an item with customizable addon? They can only do that at Cart page.
For users on first visiting, they really don't know that they can do that at Cart page, they feel embarrassed because there's no way to add quantity before going to checkout (yes, they don't know there's a way in cart page, they can quit)
Do you think this function should be available soon?