I had em for a little while, but took them off after the batteries died... which wasn't very long (about 4-6 weeks, maybe). I didn't get hit while they were on there, but then I haven't been hit since then either. They are kinda heavy and will alter wheel balance some, though I didn't re-balance for them and never noticed any balance issues. Looking back, they're gimmicky and I wouldn't bother again.
IMHO, your money is better spent on gas for another ride!