As far as I'm concerned, PrepFE has disrupted the market for FE exam preparation. It is affordable, so my department can purchase licenses for our students as part of review sessions. It is effective, meaning students spend their time actively practicing questions instead of passively sitting through review presentations. It is growing, with new features being included almost monthly. And it is insightful, providing my department statistics on each student to help us assess our program and help our students succeed at the same time.