Are they modifying URLs?
Based on the MegaLag video, it looked like they're opening a new tab with their own affiliate link, preserving cookies to ensure checkout can complete, then closing the original affiliate link tab.
Yeah I'm confused. You don't get to be the Greatest Of All Time by cheating
Friendly tip: If you're committed to sailing the seas, you can (and should) always rent a Seedbox. A lot of seedbox services also provide a way to throw up rudimentary services alongside their torrent webclient.
Both of these services for example, just have a single button to start up a Plex server alongside all the files you've already downloaded so you don't even need to set anything up other than the Plex libraries. Plus since it's already hosted, you could just share the link if you wanted friends to have access.
They're not frontends for torrents though. They're media servers just as they all advertise themselves to be. They make media files available to a network of consuming clients. Netflix, Amazon, Hulu, Disney+, all of these services also do the same. They host media on centralized servers that consuming clients can playback. In that regard, these are all self-hosted alternatives to the aforementioned.
It should also be noted that the media in question doesn't have to be torrents, they can be legitimately purchased songs that you playback via Plexamp or Jellyamp on your phone, or all the books you've gotten from HumbleBundle. They're media servers, so they're not limited to hosting just TV shows or movies.