I can see that deployment might be an issue. Yes it worked being rear ended by a car at 20kph, but will it work is all circumstances where a helmet wearer might want it to. Would it be able to detect a loss of traction around a corner and having the bike slide out from beneath you?
Also I can't imaging that a self deploying airbag helmet is going to be particularly cheap.
THe only good thing I could see on this would be to decorate it with comedy hair cuts for random inflation