From what I understand, the Ibanez ZR is the only trem that can change tunings (reg to drop D) without retuning all the other strings, and even without undoing the locking nut.

How true is this? Any other trems that can do this? like the Edge Pro?

Thanks Ahead of time!
I do Drop D on my Edge Pro III fine. I think it's because I only drop the Low e. If you drop all the strings, something will happen I believe.
Crappy Gear:
Ibanez RG350DX
Ibanez RG7321
LTD F-10
Dunlop Jazz III's (Black)
D'Addarrio .09-.46's
yah i would only drop the E too

now E to D is 1 step down right? not a half step?