Pros: - totally cute
- cheap
- useful to keep your dog visible in the dark
- really, really bright and flashy
- cute enough to be a pendant for a person!

Cons: - build quality: there isn't any back behind the pendant, so the metal contacts are exposed. No way this thing could survive getting wet.
- no on/off switch: twist the battery cap is not a way to turn something on or off. it turns itself on accidentally in my pocket
- glossy surface scratches easy, this is going on a dog it's going to get tossed around and dragged on rocks.
- no way to just be "on" it always flashes

Other Thoughts: I got this because my small dogs aren't visible at night when we walk. Cars drive too close to us. It certainly serves that purpose, drivers notice and swing wide.
However, I don't expect these things to last more than a month. There is simply no back to it, all the components are exposed, and it's a glossy surface on the front. They are already scratched, and I'm sure the first time the dog walks through wet grass it will make a short circuit.

Bottomline: If you expect to use this for a year, buy a dozen and melt hot-glue across the back. Expect to throw them away often.
There are probably better LED collars and pendants.