Flashing third brake light (in the US) is usually a dealer profit addon. Personally, I think these violate federal vehicle safety law. I'll add a link to a federal letter that I think agrees with me [1]... But no enforcement means dealers alter the wiring harness to add these on to all their inventory and add a line item on the bill. They'll remove it if you complain, but the wiring harness has been altered.

I'm ok with factory strobing on hard braking, and I think that is permitted generally.

[1] https://www.nhtsa.gov/interpretations/20288ztv