That's a ClearAlternatives taillight.
Clear Motorcycle Taillights for Honda, Kawasaki, Suzuki, Yamaha and others by Clear Alternatives
I have one on my F4i and love it. It's brighter than the stock light.
I'm not a fan of integrated signals though. I'm using the stockers with clear lenses and Sylvannia Silverstars bulbs. After nearly being run down by an asshat who wasn't paying attention, I want people behind me to know I'm turning (I had some of those tiny little signal lights). Personal preference.