I got hold of one of these from survivaldepot.co.uk to give it a try. It has a claimed output of 20 lumens for a run time of around 48 hours. It can either be clipped to a hat or attached to a finger using the provided Velcro attachment. I'll be taking it camping in about six weeks and will do a full review of how useful it was and how effective it's output is in a practical situation.
From first impressions, it fits nicely on my finger. But the hat clip, being plastic, isn't so secure. A slight flick of the hat and it flew off. The torch lights up my desk pretty well at night but it will be interesting to see what it is like outside over distances. I will also run a review of an LED Lenser K2 key ring torch which is of similar dimensions etc to give a comparison for the Nighthawk Ultralight.