I've got one (and an X5 in UV). It isn't nearly as useful as white. But I like it better at night than red or green, which have other meanings to drivers.
When I'm out walking, if I flick a blue light at someone, they will notice me against all the ambient lighting, because the blue is different. It's also good because I don't always want to light up a wide area, just check the ground near me for obstructions, and it works fine for that. It's a change from the usual. The problem is, blue degrades night vision more than other colors.
I generally carry a much brighter, white light anyway, with this as an occasional extra. Actually, I'm surprised Inova never made one in amber, which I find is the best non-white compromise color. No glare, reasonably stealthy, but pretty good for detail vision.