Black light inks are relatively new, so the risks of using them for tattoos are unknown, but so far, everything's okay with them.
The ink is permanent, although after a year, there will be no trace of the ink (if it's "invisible" ink) but it will still glow nice and bright! :)
Black light inks have UV (ultra violet) reactive particles in them, so that when the recipient of the tattoo is under a blacklight, you can see the colours shining neon-like.
If you use coloured inks, you can see the colours in regular light, but they shine under UV lights!
There IS such a thing as an invisible UV reactive ink, but I imagine it would be very hard to work with, and you do see a "scar-like" shape of the tattoo in normal light, so it's not completely invisible.
http://www.bodyartstores.com/images/store/black-light-tattoo-vin.jpg < An example of a coloured black-light tattoo. Notice how the red "shines" under the UV light, yet it looks ordinary when it's not under the UV light!
http://2.bp.blogspot.com/_UebiAKjtX9k/SFqC2g57NVI/AAAAAAAAACk/mVeP94L1ZqE/s400/black+light+tattoo4.jpg < Notice how it looks like a scar when it's not under the UV light.
They're also hard to work with, because you have to keep checking your work under a UV light to make sure it looks okay.
I wouldn't be able to tell you anything about brands, all my knowledge simply comes from the fact that I want a UV tattoo too! :D