Well dangit, I want one!
Honestly it sounds like the most interesting electronic device I've ever heard of.

I just recently read Do Androids Dream of Electric Sheep by Philip K Dick and this sounds eerily like the prototype for the emotion controller from that book.

"it just left a craving (not unhealthy, as far as we can tell) to use it again." Hmmm, "craving" doesn't sound good. How can that *not* be unhealthy? I'd like to hear about the effects of longer-term use.
Still, I'm craving one even without having tried it! Never had much luck meditating, but maybe this would do something similar.

Potential wireheads beware - the Droud is near! This sounds seriously cool, and seriously scary at once...

Straight out of Ice Pirates!

Now, if this machine could teach you how to control your OWN brain state without it, at will, it would be perfect!
Oh, also, it would need an ironclad use-case blocker so that it could not be used (with nefarious firmware from who-knows-where) to tune our human wetware to psychopathic modes.
If such a device is able to stimulate the brain to make it feel relaxed or energized I suspect it could also be used for less-useful (to the wearer) brain-hacks as well.
Imagine the (hopefully yet far-off) ability of a device similar to this to run subtle pop-up ads and various sorts of propaganda. If the capability is even remotely possible, I'd suspect that Google will be buying these guys soon.

If they had a version to lose weight, it would be a gold mine.

Sounds interesting, but I'm wondering about the side effects of messing with one's brain.
Developing psychological dependency?

Harriett Russell, there's nothing wrong with craving. How you address those cravings is what matters.

LIFE, for every cell in the body means dynamic relaxation and tension by inner "intent". Everything that does something to make this easier or less needed will weaken or restrict, whether you're an amoeba or a man, body and mind. This is why drugs, laziness and avoidance lead to lessened capabilities and ultimately DEATH. Unless of course it's incapacitation in need of for example insulin or prosthesis. Thync seems to belong to the avoidance or drugs class. Accept, adapt and, commit yourself to reality is what you need to get a satisfying life.