The Toplight Line Brake Plus senses when the bike slows under braking and glows brighter. It does this by monitoring the AC frequency from the hub. During braking, the AC frequency slows quickly, and then makes the LEDs pulse or flicker, hopefully getting the attention of that fool in the jacked up SUV behind you.
The Toplight Line Brake Plus has the usual standlight, and mounts to the rear of many racks. But unlike the other rack mount taillights, the Toplight Line Brake Plus only has mounting bolts 50mm apart, unlike the others which give you the option of either 50mm or 80mm. This taillight is narrower (92mm) than any other rack mount B&M taillight, making it more suitable for some of the new narrow racks. Even though the light's housing is narrow, the light you see at night is much larger than with other taillights.
There's a red tab on the bottom which you can press to switch off the standlight when you park the bike. It does this by discharging the capacitor.