As the current docs have said they are a very useful tool and the associated training is good for everyone not just divers. As has also been said they are not that useful in a drowned diver scenario, the one I was involved with the biggest issue was the inability to clear the air way and by the time appropriate gear arrived it was too late. If truthful it was too late by the time the diver was recovered. There was an anaesthetic ITU consultant present who lead the proceedings was prepared to call it and stop but local ambulance protocols said otherwise. Yes they are useable in wet conditions.