The SEO problems and Blog checkers in Plug in SEO Free all work on any public website. Most of the advice is Shopify specific, but they will return actionable results on other platforms.
The Plug in SEO Plus upgrade is only available for Shopify at this time.
Are you on Bigcommerce, Magento, WooCommerce or something else? Let us know and we'll drop you an email when we launch there.