ScottyP said:
The Phottix Mitros+ flashes (the "plus" is important) has a well-respected Phottix Odin transmitter and receiver built into it. It does a couple of things the Canon 600 can't do, including second curtain sync off-camera. It is somewhat less money, though not as much less as before the Canons recently started appearing at cut rates.
The Canon RT system can do second curtain sync if you trigger it with a Yongnuo YN-E3-RT, but as ScottyP points out, not natively. Though I have yet to see a good example where off camera second curtain sync has been critical.
There is a huge amount of
misinformation out there about all the various flash products, including the Canon RT system. Like Alex thinking the RT could not sync at 1/8000, or that you lose one stop of sync speed, or that you can't do remote second curtain sync, that the 600-EX-RT is not backwards compatible, etc etc.