Just so happens i was talking with my zoll rep today.
my service has had them for several years now. They only work for a very specific pt type (150-250 lbs, 5'5"-6' tall, otherwise relatively health person)
The pt has to be securely strapped to the devise. Zoll is going to be shipping out a lithium battery in the coming months, to take the place of the current batteries which need to be rotated daily. It's a good product, does what it's suppose to do (with practice)