I created a custom Product Property named "style_number" using the CRM Object Properties API. I can see that this property has been successfully created when I get product properties via the API, but when I view or edit a product in HubSpot, this custom property is not visible. Hidden is set to false for this property as well.
At this time, custom product properties cannot be viewed or edited on the front end.
I would expect your properties to appear in the interface once it's possible to create custom product properties in Property settings.