Just recently I had the opportunity to try the previous model Speedlite Transmitter on my 5DMk111 using two 580exII flashes. It was great for using flashes remotely for macro work. I am considering buying one but have discovered the old model is dearer than the Canon ST-E3-RT Speedlite Transmitter. The old model is also hard to get. The Canon ST-E3-RT Speedlite Transmitter is about $350 locally.
Is any one familiar with the new model? Any comments or suggestions?