Shoppdeveloper.com

By default the Shopp breadcrumb will display “the path you followed to get here”. And frankly, that is 
what breadcrumbs are meant to do. However this means when someone enters one of your product pages using 
a direct link, the breadcrumb will be empty. It will just show the link back to the main Shopp page. 
With this plugin installed you can use breadcrumbs that show “where you are” in the hierarchical 
structure of categories.

Shopp Default Breadcrumb Extender

Add hierachical breadcrumb to your Shopp webshop product pages.

manipovore

MP Post Navigation adds navigation links on a post to the previous or next post of the same current category. 
Text links are useful for SEO and << – >> add ergonomics and design. It is optimized for responsive.

MP Post Navigation

The plugin adds navigation links between articles of same category. Optimized for responsive, SEO and ergonomics.

Shopp Default Breadcrumb Extender vs MP Post Navigation