I've not seen flashing dog collars in use before until last night when I was on a dog walk.
A lady a few doors down has them for her dogs and one of them is black. We live with a bridal path behind us, so every cyclist in the world seems to use it when they finish work. Although my dogs have never been hit I could understand how people cannot see the dogs whilst in the dark. It was nice to see that even in the dark the cyclist still saw the dogs and missed them.