Product Options and Customizer
Create extra and unlimited product options (price per option)
Seamless workflow: use directly in Shopify admin
Up-to-date tech: works with the latest themes
It doesn't work on Shoptimized Theme. But for standard (old Themes) is good. A lot of features.
Quirkshop Com Au
Did not work for Jumpstart theme (a shopify theme) and I felt it was a bit of a hack job, with a product that shows up in your store but can't be deleted. However, maybe it works well for other themes. Wasn't right for me unfortunately.