That choice is probably the brightest when viewed directly from the rear
I use Planet Bike Super Turbo Flash. Brighter from an angle but not quite as bright as the Hotshot from a direct rear angle. It has a decent battery life.
Turbo Flash is great for the nighttime but not good enough for the day. I have regular Superflashes & use them as back up lights. One can only squeeze so much from the meager AAA alkalines. AAs are a different story. Perhaps I'll get the Serfas as a rack light for my utility bike.