I don't know if anyone has tried. I registered my voucher the old way when you still could...not sure if it possible now.
I believe the new site will allow it, as a voucher is basically like a will call order, and they will accept will call order numbers.
No idea what that will buy you yet since it's all meaningless until you are permitted to use Fastpass+.
MDE/MDX works fine* in the parks, and anywhere else, actually...it's the wi-fi in the parks that's crap. But if you're fine with using mobile data, it seems OK.
hopefully its working 100% better when we go in August than when i tried using it in March, cause it was 100% useless then.
MDE/MDX replaces Mobile Magic.
MM is dead.
hmm, i just clicked on MM and it appears to still work.
* Fine, in the sense that "slow, painful, hard to navigate" is Fine.