It is probably good for my pocketbook that I use a rack bag on my weekend fun bike, so there's basically no practical way for me to usefully mount one of those spiffy (but expensive) radar rear lights. I keep eyeing them when I see people with them, though, because they do nifty things.

(I was behind a pair with them on my ride home today, so I got to see their lights start blinking as cars approached all of us from behind.)