According to it's creator:
By the looks of it (not tested), it uses iNotify (filesystem signals updatess and passes them to applications), so you will get real-time updates.FSearch is a fast file search utility for GNU/Linux operating systems, inspired by Everything Search Engine. It’s written in C and based on GTK+3.
Note: The application is in an early development stage and still considered beta
IMO a good initiative, that deserves some support.