I ride a lot in heavy traffic, and there's a lot of dozy cage drivers with cell phones, eating and generally not paying attention. NZ has just changed the legislation allowing overseas approved brake light systems, so I splashed out and bought a Kisantech bulb for the taillight. It has flasher circuitry in the bulb base, which simply replaces the taillight bulb. The light unit is replaceable, and the unit comes with a spare (I didn't realise so ended up with 2 spares).
A minute to instal, and it starts off with a frenzied flash, slows and then stays on as per normal so you aren't pissing people off stopped at the lights. I like it. It's a shame NZ doesn't allow headlight modulators,as I'd get one if I could.
The site is: https://www.kisantech.com/view_product_pop.php?product=20W-D