Trouble is, these beacons come preset to a particular blink pattern, and when you buy one (ten, fifty) you're probably not going to bother to change the blink pattern in them all. What if you forgot to do one?
So what happens is that your building is synchronized to GPS, and so is your neighbour's building, and so is _their_ neighbour's building. The whole city flashes once every two seconds, like clockwork.
Completely negating the whole point of having one blink-pattern per building, and rendering aviation around tall buildings unsafe again.
It's an accidental own-goal, brought about by the efficiencies of global, perfect, timekeeping.
(end)
(Postscript: a few of us here on the Fedi worked this out from first principles after someone noticed that the lights on several buildings in their city were all blinking together. It was a great piece of detective work.)