The above answer is yes. For the EX550, you'll get TTL functions.

Do note that the Phottix Universal TTL cord duo can trigger two flashes at the same time, with more details at http://www.reddotphoto.com.sg/ecomme...d=224&catid=15

Another possible setup using two flashes would be: using the PC Sync output from a camera (for eg, from a Canon 7D) to trigger one flash and at the same time using the TTL cord duo to trigger another flash unit.