Canon brought out the Very Expensive 600EX-RT flash which is capable of being either a radio or IR master. That's really nice but, AFAIK, the 600EX-RT is the only unit capable of being a radio synced slave. That means in order to take advantage of the 600EX-RT radio sync capabilities, you need to have at least two of these expensive units.
Canon has always had Master Units (550EX, 580EX and 580EX-ii) which could be used with less expensive units like the 420EX, 430EX and 430EX-ii as slaves. This was quite a savings in both cost and weight,
I have not been keeping up with Canon flash offerings lately. Does Canon have a less expensive radio controlled, slave unit in line with the previous offerings of relatively expensive master and less expensive slave units.
Finally, (I should be able to figure this out myself) can I use the 600EX-RT in IR master mode to trigger the optical slaves of studio strobes? I have a small IR trigger which will do this but I am wondering if the 600EX-RT will accomplish the same thing...