This is the used B2 250 AirTTL Power Pack, a part of the expanding OCF (Off-Camera Flash) system that includes the optional B2 flash head.
Like another family member, the B1 battery-powered monolight, it boasts full TTL operation with Canon and Nikon cameras with the purchase of an optional Air Remote TTL-C or TTL-N. Just set up your lights, point, and shoot – you’re first shot is usually a keeper. It’s actually that easy.