How can I get featured paypal shop app products on homepage?

Is it possible to filter by a custom field at all when using the old Paypal shop app?

I want to allow editors to choose featured products for the homepage. When I try to filter by the custom checkbox I added to the products.html shop template, I don't get any results coming through on the homepage. Filtering by standard fields works fine.

Perhaps there's a method I'm unaware of to get featured paypal shop app products on the homepage? Or will I need to use the new shop app that's in beta? (I'm doing my first Perch build so hesitating to use the beta shop app for now).

Thanks