I know this will stir up a frenzy, and I am not making an opinion, but I thought I would share some info I just read in the Driving section of our local newspaper.
Apparently Mercedes Benz issued a proposal to the DOT and NHTSA to equip their vehicles with brake lights that would flash when a driver made a panic stop. The Feds turned down the proposal, skeptical that they would provide any safety benefit, and Mercedes was unable to provide any proof that there is. It added that currently, flashing brake lights are illegal.
Despite the many folks who say "they have checked on it and found they are legal", apparently they are not. The aftermarket is bound by these same laws too, regardless of whether you have been using them for years and never been stopped.
Just thought anyone contemplating the addition would want to know. Now try not to kill the messenger.