Eternal Velocity pointed out some impedance irregularities in a graph he posted for the Faital driver
I wouldn't call them "irregularities" - in fact "regularities" might be more accurate. It's the acoustic elegance drivers which are irregular!
For reference, Troels Graveson has worked with some of the finest Hi-Fi drivers on the planet from Scanspeak, Seas, etc. When it got down to developing his own driver (A High Sensitivity Seas Excel unit for the most part), which he (of course with bias) considers his personal favorite, the measurements actually showed some "impedance problems".
What you have to remember however, is that a more sensitive driver will apparently magnify the impedance issues. The impedance can make you panic, but that doesn't mean you should panic. Even this scanspeak revelator shows a pretty big bump:
And it's not as signfiicantly "visible" in a lower efficiency design.
So I do want to apologize if I gave you any apprehension. The acoustic elegance drivers are certainly irregular, but i'm not 100% sure any of those things are audible once linear response is carefully addressed.