I've always been in the habit of showing a little brake (by tapping the rear lever) whenever engine braking. It's become habit.
My friend and I were ridding behind another rider on some dirt roads recently and we noticed he had some red led lights that seemed to be randomly flashing. For the next 30 minutes or so we were conversing via intercom on what the heck they were. As I had heard of these led's that light upon deceleration, that was my first guess. But, they did not seem to coincide with his deceleration. Sometimes they did, but just as often they didn't. I concluded that they were just set to randomly light up - to keep a driver behind alert maybe. Anyways, when the guy stopped I asked him and sure enough they were deceleration lights. Decelerometer is what he called it, I believe. So i'm guessing his type works on some kind of tilt sensor (mercury switch?) that detects the forward tilt on deceleration. As I mentioned, we were on dirt roads and they were a bit rutted as well as hilly. All that bumpy and hilly stuff was just sending the sensor into a tizzy. Did not seem like a worthwhile product. Led flashing brake lights combined with showing some brake is much better/safer IMHO.
2014 DL650 (sold)