I have the Bontrager Flare RT & the Varia 510. In my informal observations the Flare RT appears somewhat brighter to my eyes in normal flash mode. I set up both about 100 yards away and on a bright day the Flare RT was definitely more visible than the Varia. But, when the Varia detects the approach of a vehicle and increases its flash frequency and intensity they look pretty close to each other. Close enough that I don't think I can tell a difference by eye. Plus the Varia has much better battery life even with the radar. Of course it is quite bit larger and a 48g heavier.