Oh yeah they work. I have the little round one about an inch diameter, and it works great, and the battery has lasted three years so far. Lives under my rear seat, getting mud thrown at it all day. It works. Its bright. It is sensitive but does not go bright on a false trigger.. it works good like an actual brake light.
Smart lights are cool. So are smart turn signals ( wireless turn signals)... you dont have to go through the wire harness. This is the one I got.
https://www.fenixdeal.com/rockbros-bicycle-smart-auto-brake-sensing-light-ipx6-waterproof-led-charging-cycling-taillight.html