Saas vs Plugin
I read this explanation in facebook.
SaaS means you can put it on any website, like Shopify, Squarespace, Wix, or even static pages. SaaS also means that your “platform” doesn’t have native access to the data, so you’ll rely on extensibility of the saas to get your data out. Plugin means that your data is native to the platform (in this case WordPress) so it likely (although not always..) easy to get that data into other aspects of that platform. It also means that if you buy a WordPress specific tool and decide to open a Shopify store in 6 months, you can’t put pop-ups on it (without buying something else).