I wouldn't sign up for a VPN based out of the UK. Frankly, May scares the shit out of me - her ideas about regulating communications comes across as more than slightly fascist.*
* My head of state is He-Who-Must-Be-Impeached; so I'm getting more familiar with fascism on a day-to-day basis. (I won't even use an email provider located in the US due to the way the government over here behaves).
Don't forget about the Semites. While the diversity would be great, but you have to keep in mind that many of them won't work from sundown on Friday. They'll also skip out on all 12 days of Ramadan.
I think the success of those companies is due in no small part to the fact that they don't force account creation for passive use. If wikipedia presented me with some bullshit intro to an article with a promise to be allowed to read the whole thing with an account I'd either go to the competition, or sign up with bogus account info, and then copy/share the article with whoever I can to save them the hassle of making an account.
I'm currently taking a discrete mathematics class that Applied Discrete Structures by Alan Doerr and Kenneth Levasseur (http://faculty.uml.edu/klevasseur/ads2/). It's freely available, though I recommend steering away from the PDF on their site as it's got quite a few errors that are corrected in the source on Github.
* My head of state is He-Who-Must-Be-Impeached; so I'm getting more familiar with fascism on a day-to-day basis. (I won't even use an email provider located in the US due to the way the government over here behaves).