The friend codes are actually recruit a friend codes. They honestly don't offer any benefit to the new subscriber they just offer rewards to the person giving them out to others. Its a promotion to get more people on the game lol. So you just get a 10 day trial. Basically if you want to try it out and you think you might subscribe let me know ill send you a code to get your trial.
Yeah, the game is a bit tough on some computers. And yes it takes up a lot of room. If you don't have a compatible video card don't even bother downloading the trial. It wont even let you play if your card isn't as good as the ones on the list.