I think like all sparks I'm totally against them. Most of us here understand what the limitations of these things are, but they are not aimed at our market they are aimed at the DIY end, and they are sold mainly as votalge testers, though the product name is voltage indicator.
The trouble with them is it encourages the not so savvy DIY'er to undo something and test to see if it is live, and if it is then you have the situation of someone poking about into something he doesn't understand, and using himself to make a circuit, they are horrendously unsafe in this type of situation, but there again so is a car if your not trained to drive.
There was a post on here a while back where someone was testing to see if his meter was live by using a Neon, it makes me shudder to think of someone poking about at a meter armed with just a neon screwdriver.