I don't worry about synchronizing flashing lights. I just use whatever I have available. My theory is two or more lights are better than one, and it's the physical separation that helps drivers quickly estimate our distance, direction, speed, etc. Unlike motorcycles we usually can't separate lights horizontally, but can mount them on the bike and helmet. That's what I do.

A few years ago I noticed folks riding around town with bike and helmet lights. They really popped into attention amid a cluttered background. That persuaded me to do the same.

But the best attention getter is wheel lights. Those colorful LED wheel lights beat anything else I've seen in many solo and group nighttime rides. The wheel lights don't even need to be particularly bright. Cyclists are often practically invisible from the sides, even when they have head and tail lights. Wheel lights solve that problem. I've noticed that many times as a passenger in motor vehicles, seeing other cyclists.

Synchronized lights sound appealing for fastidious detail oriented people but in practical application I doubt it matters as much as having two or more lights of any kind.