I use them because my seatpost is taken up with my seatpost bag and a water bottle holder for my two water bottles. They are pretty bright, and I like how they blink. You also can choose the option to have the light not blink too. I think I've got some visibility because of them.

They are on sale at performance for 14.99. I got them for 9.99 on sale during the double points, so check and see if they're going even cheaper.

Koffee