Based off my 3 days of research into the topic, yes it is free but you're at the mercy of seeders and active torrents. Isp's also may not like you using the service as it's torrenting and your usage of the service is very visible.
The paid aspect of it comes from this service called Real Debrid which basically is a middle man that downloads all the stuff for you (or 99% of the time already has it downloaded) and then will send it to you via an encrypted connection at whatever max speed your internet is. It allows for smooth, 4K HDR, no buffering streams just like you'd get from Netflix and only costs 33$ a year. Real Debrid can also be used to download any torrent in existence at max speeds.
Changed my life. Literally a 4 click setup, never done anything easier. Just search for "Stremio, Torrentio and Real Debrid guide"
slifer