Pros: Nice and small for a keyring
Good build quality - Mine has been attached to my house keys since last August and no problems.
It really does glow :)

Cons: The glow is not very bright. It must be in a dark area to see it.
Only came in a bibblewrap bag (no box) so if giving this as a gift, it looke really cheap and the person will not know what is so special about it!

Other Thoughts: It looks like a cheap glow in the dark keyring, until you see the glow does not dim like other glow in the dark things do.

Bottomline: Useful to find your keys in a dark room!! Might be a bit expensive for its size, but hey it is still glowing all these months on!

Pros: - Interesting gadget for geeks
- Makes finding my keys easy at night when the lights are off
- Interesting talking point
- Should glow 10 years

Cons: - Not very bright, lights have to be all off in the room to see this actually glowing
- After a couple of months of being on my keychain the epoxy seems to be cracking at one end so won't be using it anymore as worried the tritanium will leak out

Other Thoughts: Ok thing to help find things in the dark, but needs to be dark dark not just dim room.
Pretty small too so you need to know what your looking for.

Bottomline: With the risk of it splitting and the tritanium leaking and although I'm not sure how much is this item rather not risk it so not using it any more.

Pros: -It doesn't need batteries, manteinance or charging, it just glows. For years.
-It's really small, can be attached to anything without adding bulk.
-Bright enough to be spotted instantly in a dark room.
-Green is by far the brightest color these come in, closely followed by yellow, then orange, blue and white (dimmest).
-Useful for flashlight mods.
-The vial is 1.55mm x6mm (about 1mm longer than usual).

Cons: -Plastic gets scratched easily with keys and other items.
-Cannot remove the split ring without scratching the plastic.
-It's hard to take out the vial (to use it for flashlight mods), the plastic capsule will be destroyed in the process.
-With time and banging up against keys the plastic will develop cracks at the bottom of the capsule (though the vial is also glued inside, so it won't fall).

Other Thoughts:

Bottomline: Keep in mind these will not light up your whole room! It's about as bright as the minute hand on a wristwatch after charging.
But... attach one to a flashlight and keep it on your nightstand, or a shelf in your garage. Attach one to your keys, and you'll always be able to find them even when you drop them in the dark. Attach one to the zipper of your bag, and you'll be able to find/open it after the cinema's lights are off.

Pros: -Good price, for this particular item.
-Has keyring, so can be used as keychain.
-Radioactive - a cheap and easy sample to test your Geiger counter with.

Cons: -Only lasts for around 10-15 years.
-Slightly too dim.
-Illegal in many countries due to "careless use of radioactive material."
-Build quality is questionable, but seems okay.
-Radioactive. I tested it to make sure.
-Don't sleep next to it. =P
-Don't put it in your pocket.
-Don't bring it to the airport.

Other Thoughts: This is radioactive, illegal, and is dangerous. Not that dangerous, but being an isotope of hydrogen, can bond as hydrogen in the body.
If you break it, open all the windows and leave the area. Handle it like a broken mercury-vapor light bulb.
Tritium is also used to boost the yield of nuclear devices.
I got mine for free because DX gave me store credit for a broken item.

Bottomline: There are better light sources. I would recommend buying this only if you have a definite use for it.
If you just want a light, go for an LED instead. It's brighter, it works well, and there is no fuss.