I am the author of this software along with my co-founder Dimo Stoyanov.
As I assume you know Popcorn Time is based on peerflix, which I contributed on right after it started as a part of our development on Stremio (formerly Cinematic), which started in 2012.
Besides that, there are no relations between the products.
As to why is it paid - the product is much more powerful both in terms of content (automatically scraped) and in terms of features (what you're actually paying for).
Hope you give it a try. Best, Ivo