But, why did Canon leave out an AF assist beam on the transmitter??
Many people seem to be wondering about that - I would rather get another 600rt than the rather expensive transmitter due to the missing af beam (which works excellent btw, seems to be better than on my 430ex2). Maybe the transmitter is so small that the beam wouldn't fit? Or they have an updated transmitter in the pipeline, together with the rumored 660rt with ettl-iii (featuring remote 2nd curtain sync :-))?
That's what I did. Went with 2 of the flashes (at a considerable cost ) but I'm really happy with the performance. I love the master/slave and dual flash, as well as the Manual settings, semi-manual settings are amazing, and last but not least I love the exposure bracketing/compensation.
Using a 600 just for it's AF beam seems like a waste, but in some instances you need the AF beam. Having two 600s and the transmitter gives me flexibility.