Not much is known about the Faustus Interceptors other than that they are an attack craft used for long-range patrol duties which operates as early-warning detectors for Imperial fleets (Sort of like patrol boats and coast guards of today only you know, in SPAAAAAAAAACE!). Due to this, they possess onboard astropaths who probably prefer to be on the safety on a spaceship than a squishy fighter. Their job is to secure long-distance communication.
Faustus interceptors despite their size, are surprisingly powerful and fast and can be armed with a variety of turreted ballistic cannons and a forward-locked plasma gun "array". While this makes them arguably superior than a Fury Interceptor, the fact that it needs its own on-board astropath makes the Faustus expensive and thus, unreliable. If anything, their rare materials needed to house the Faustus makes the Mechanicus extremely anal about it if something goes off in its adventures.