VPNs are not secure, it doesn't matter if you pay for it, get it for free, own it, piss on it, etc. do not buy jimmu's garbage VPN or whatever the fuck that thing is. people using VPNs for torrents are basically just temporarily fooling some RIAA/MPAA bot that sits there collecting IP addresses of seeders and downloaders, but the NSA and other organizations know about it and most importantly the VPN probably has logs of it (inb4 "lol i totally don't keep logs bro! just trust me!"). better off not using torrents or using I2P torrents only, or move to place where they do not give a shit about copyright and ISP simply does not respond to dumb "give me money" letters.
some people use someone elses server for like actual work, that sort of thing, you know like software projects or hosting a website or something. thats what its mostly actually for.
take a look at how anonymity networks work, its like five minutes of reading for the tl dr to get an idea of how Tor works at least. the rest basically suck and are unusable buggy unfinished insecure bullshit (also known as a research project), except I2P is kinda useful (but not for web browsing) since its been around for a while and the software is a little more stable than some of the other Tor alternatives.