It's not a flanger, but more of a swept filter/phasor effect.
Picture a phasor that's way more vowelly sounding, so it ends up going "yoyoyoyoyoyoyoyoy"
It's very vocal/formant sounding, and not like a typical phasor. It's a very cool effect that not many other pedals with give you.
They are huge, hard to fix and way too expensive.
Line 6, are you listening?
(yes, you are!