No, Five Nights at Freddy's is not on this. There's a version that was being worked on, but it got shut down for legal reasons. Still, there are plenty of great games you can play on SmileBASIC, so it's definitely worth it!
Yes, there is a huge library of content that you can download, some that could be worth 1-2 dollars on their own. Plus, with 176 Programs pages and 85 Game pages (games count as programs) on SmileBASIC Source that may be worth at least 50 cents, there is so much value in this program from the users themselves. Plus you can learn to program if you want. That's also worth it.