Approval for Global Entry is for 5 years. Then you have to renew online. When I renewed earlier this year the web site said that I would need to go for another interview with Customs & Border Control but 3 days after I completed the online application process and paid the fee I got an email saying "Congratulations" you are approved for another 5 years and may use your status immediately. The program is definitely worth the $100. If you have an American Express Platinum Card and use it to pay the fee, they reimburse you for the $100 so its essentially free.

Pre-Check is never guaranteed as they randomly force people thought he full screening process. I find that it works roughly 80% of the time.