By your description it sounds like the exact same bulbs my friend has on his ninja. 2 bulbs that spin non stop, and flash when braking. anyhow they are never synced up, but the worst is its so distracting in general, that when he finally brakes you don't notice it. You get zoned out, and try to ignore the spinning brakes, so when he finally stops and they flash, you don't notice it. Mainly because they aren't any brighter when braking...
I've never rammed him, or got that close, but the lights drive me crazy. I would suggest against them for that reason.