They clarified FBA. Still wondering about this. I actually use this...sorry.

Wait... so what's the question?

EMP Device has the same wording as Feedback Array (ie. "During the combat phase, instead of performing any attacks, [do stuff]"). The FBA ruling therefore would apply here, so no, you can't use EMP Device while cloaked.

Its not specifically stated, and feedback array has more potential abuse as it deals an unavoidable damage and could be used 5 times theoretically.
EMP Device causes no damage, and is single use, due to the discard requirment. Because of this I think EMP device is still legitimate to use.

Also in a furball feedback singles out a ship of your choice whereas EMP hits everything at range 1.

Personally, i reckon you should switch the cloaking device for a deadmans switch, so either the enemy shoots the quadjumper to prevent it lowering their agility and takes one damage or your other ships get easier shots and the quad gets a range 1 unmodified, 3 dice attack, against an agility impaired ship.

Unfortunately, "I don't think it would be overpowered" is not a legitimate rules argument.