What does an ST-E3-RT transmitter in a hotshoe do, that a master 600EX-RT can't

[Wick]

I like the ability to control the speedlites from the camera menu itself. Depending on the camera position this can be a real advantage.

I was lucky enough to get the STE3 for $309 so it made sense to get that instead of a 600 just to sit on the camera. I use the 600s I manual mode, and I can vary the output power of each right from the camera menu.

What I have not been able to do (perhaps someone here can help me) is to turn off one of the flashes from the camera.

 

[Digirati]

I've had 3 600's and 1 ST-E3-RT and they've been flawless (started out using a 600 as a trigger).
I was on several shoots a few weeks ago with several versions of Pocket Wizard's and they often didn't fire and, and at one point, stopped working altogether that required shut off of everything and do a reset, and were very undependable overall. The last thing I want in a shoot is to miss the shot due to equipment failure as there are enough variables to fail including shooter/talent.

When a piece of equipment just works and has proven to be perfectly dependable, I'll use it over and over. Yes, I wish it was a little less expensive, but getting the shot pays for itself and for more jobs.

 

[Wick]

I'm hopeful about the rumor of a smaller and less expensive flash unit using the radio system. I have an STE3 and two 600s and can't justify a third one. But something in the $350-$400 range with less output would suit me perfectly.