Have you used either/or any similar extruders? The flexion isn't too different from any other extruder, the brush is there because the deeper hobbed gear grinds harder filaments like pla and abs (non flexibles) a bit more, and it has a fixed, positive pressure idler rather than a spring loaded one. That last feature I find pretty cool and I'll make sure my hot end can do both spring pressure and positive pressure and switch between them easily.

As for the gearing, I'm not sure how useful it is, what positive effect does it have on prints and is that finer resolution noticeable in the end result? Again, I suspect it shines more at higher speeds where you need to push more plastic through the extruder.