Out of the only driver pics that I've seen, there were 5 different codes, but their meanings are not yet clear.
This is likely the only reliable info on the different known versions:
021 - black magnet + white baffle damping (acoustic lens unknown) (no measurement) (from 'The Legendary Prince' thread)
121 - black magnet + black baffle damping + white acousitic lens 'donut' damping version (huge rolloff in bass and treble)
521 - metallic magnet + white paper damping (no acoustic lens damping) (neutral)
(I own this one)
531 - appears to be the same as 521
(@Feilong4 owns this one)
721 - metallic magnet + white paper damping (acoustic lens unknown) (no measurement) (from Japanese blog)
Seems like if it starts with 5, it should be a keeper.
From visuals alone, 7 should be fine too.
Since
Purk owns the one starting 021, it's probably safe to assume it's also a keeper.
The only known one to absolutey avoid is the version with black baffle paper (121).