Eddie used the original MXR Flanger to create the signature tone in his song "Unchained". To celebrate the 35th anniversary of the flanger, Dunlop gave it a design much like the most popular version of Eddie's "Frankenstein" guitar and added a button that replicates the exact settings Eddie used in "Unchained".
This pedal is awesome, period. I've tried lots of popular flangers (Boss BF-2/3, HF-2, EHX, Ibanez, TC, other iterations of MXR, too) and EVH version - as far as I can tell from my humble experience - is the best flanger I've played so far. Very little noise, tweakable as hell and sound quality is brilliant. Useful settings I found so far: 1) Subtle chorus into flanger (Manual 10:00 Width 10:00 Speed 9:00 Regen 7:00), 2) Intense swoosh (Manual 10:00 Width 2:00 Speed 3:00 Regen 4:00) Of course there is this "Unchained" button which gives you that unique evh tone; I like it but it is not definately the best setting that you can get from this unit.
Do not hesitate to get it - you will not regret it.