I photograph a lot in aquariums and was tired with a TTL flashing cable unleashed, you must be connected in the truest sense of the word, so I was looking for a cheap but useful radio transmission system, TTL transmission would have been desirable but not mandatory, so I ended up at the radio transmission systems by Yongnuo. The RF 603 II I have chosen because it fit in my budget and you can use the respective device as a receiver and transmitter, I must resign speed TTL to the system and control the flash so manually can did not bother me, Blitz slightly lighter or darker rules manually finally no problem;) So said and done and ordered, the next day it was there and I must say I was just excited for the money of the processing, the battery compartments easily go on and on (what with cheap products, unfortunately, often not the case) allow the switch to provide easy and raced also felt good and it has a Metallblitzfuß, which is nice stable, also the casing is well made and well rounded no sharp burrs and edges. the Bediehnungsanleitung is unfortunately understood easily only in English, but even with my limited knowledge of English, as also well illustrated, the first first time synchronize the receiver and transmitter to the radio channel, short in both devices, the mini SMD switches in the same position bring, I must say, the switches can be quite difficult to push and you are afraid to break something, then set the selector switch on the unit to the camera and the flash on TX and TRX can already going to go, I can only say I am delighted with the device, it always triggers reliably, whether posted on the aquarium, in 10m distance (further I have not tested), or even through a wall. Unfortunately, it has one drawback, which has not really bothered me, however, to note it does not work with all flash units , With my Metz 44AF 4C it does not work unfortunately and fires the flash does not, with the hotel offer of Yongnuo he works in manual mode the flash perfect. I once they work together a list of flashes, which I read on the net with the system Yongnuo: YN565EX, YN-468II, YN-467II, YN560 II, YN-460 Metz 58 AF-1, AF-48 1 Canon Speedlite: 580EX II, 580EX, 550EX, 540EZ, 520EZ, 430EX II, 430EX, 420EX, 420EZ, 380EX Pentax AF-540 FGZ AF-360 FGZ AF-400 FT, AF-240 FT Nikon Speedlight SB-900 SB-800, SB-600 (Auto Standby off), SB-28, SB-27, SB-26, SB-25, SB-24 Olympus FL-50, FL36 I use the system for a month now and use it almost every day, the batteries (2x AAA per unit), I have not need to replace, so it works quite power efficient, failures or dropouts, I had to complain in no time. All in all, the system gets from me a fat recommendation for all who are looking for a cheap and good radio transmission system, as long as they do not need the TTL transmission