After reading about the 470EX-AI, the AI is the difference most obviously. It clearly states on the Canon website or on Amazon that this flash calculates the distance between the subject and ceiling and adjusts the angle and flash strength to match. It also maintains angle as the camera is moved apparently. Seems cool. Not clear if this outputs as much flash light/power as the 600 and assuming the AI uses the batteries in the flash, this will likely decrease the length of time batteries can be used in the flash, and also may not be best when subject is moving quickly, or if the photographer moves quickly (as in wedding or sports photography). As photography is a "Sum of all parts" game, putting your flash in control of itself may not be the most dependable or desirable option for pros.