Clever, but so small that only a driver who was very close could possibly hope to read it. To everybody else it's just a normal-ish tail light.
Also, the amount of light varies based on your speed, and will be quite low at some speeds -- 1, 7, 11, 17.
This can put your speed on the wheel, where it at least has enough room for people to see without being right on top of you. I'm not sure if showing people your speed like that has significant safety benefits, though I can think of a few situations where it might, and having lights of any sort that are clearly visible from the side certainly does.