Don't get me wrong. The Canon 580 EX is a great little flash. If you want a unit that can double as a studio light the Quantum is a great unit. At the time of writing this update I have sent my original T5D in to Quantum to have the Qnexus module added. The following text is from their website on what this does.

When mounted to Quantum's new-generation Qflash 5d-R flash units, this ingenious receiver/decoder "reads" wireless TTL signals directly from Canon and Nikon shoe mount master flashes. It integrates multiple high-power Qflash 5d-R's into Canon or Nikon wireless TTL systems where they act as dedicated, full-function remotes controlled totally from the camera's flash menu. Qnexus supports all Canon and Nikon wireless flash functions including Manual, Automatic, TTL and TTL-Ratio.

A Qnexus equipped Qflash 5d-R produces 150 to 400 watt-seconds of beautiful studio-quality lighting (models QFT5d-R and QFX5d-R respectively). Qnexus greatly expands creative options for portrait and event photography. For example, photographers can make a great portable portrait set-up by using a Qflash in a softbox or with an umbrella, as the main light source, and use their Canon or Nikon flash for fill. Or, for those tricky, large group photos, they can use any combination of Qflashes with camera manufacturer's flashes as remotes, all controlled by a Nikon or Canon wireless controller. Qnexus/Qflash adds both power and versatility to the system.