@peterjduffy, I think it’s very difficult to say, from a CEFR perspective, how far PP materials can take you. On the one hand, so far, the website content hasn’t been developed in light of CEFR standards. On the other, even though PP has a wealth of resources, including some human support to help people connect the dots, we also have to rely a lot on people’s ability to study independently and to do so in a way that covers the whole range of aspects that constitute fluency (grammar, vocabulary, listening, speaking, etc). Some will do it better and faster than others, even though, in general, I think many people appreciate the fact that they can have a kind of choose-your-own-adventure approach to PP.
If I had to make a quick non-binding guess (), the units alone might leave you somewhere around upper A2, overall. If you add to that all the Learning Notes, verb exercises, forum posts, videos, shorties and long podcasts, I’m sure you can go further over time.