Just posted: Canon Speedlite Transmitter ST-E3-RT Review
If you read the Canon Speedlite 600EX-RT Flash Review, you are already familiar with the ST-E3-RT. Basically, extract the 600EX-RT's radio wireless system, LCD, switch panel and foot, and put them in a housing just large enough to hold those parts and two AA batteries. What you have is an ST-E3-RT.
The ST-E3-RT is a great addition to a radio wireless flash kit. For an instant kit, get the Canon ST-E3-RT Transmitter & 2 Speedlite 600EX-RT Kit at B&H for $1,119.95 with free shipping. Basically, you are buying an ST-E3-RT and getting two 600EX-RT Speedlites for $416.48 each.