I currently have both the Helite Airnest/Turtle (street) vest, and the Helite GP-Air (track) vest. I crash tested the GP-air vest at a track day about 2 weeks ago, lowsided at maybe 40 mph, resulted in me sliding and rolling. The vest properly inflated, I got up with no injuries and only minor scrapes on the vest. I definitely believe that the vest helped keep my fancy new helmet from contacting the pavement - I couldn't believe that my helmet was unscathed. The vest is able to be recharged in only a couple minutes with a $25 air canister.
I am a believer in them now, I am definitely going to try to wear the Helite more on the street. The Airnest/Turtle version works great for upright bikes like a Strom or my Tiger. (I wouldn't recommend it for sportbikes as the external canister area will scratch the tank and interfere with your body position on left turns.) Its also available in hi-viz. Yes it is expensive, but comparable to the cost of a high-end helmet, and certainly cheaper than an ambulance ride. In my case, the vest prevented me from needing to replace my helmet.