Canon ST-E2 - Transmitter - for EOS 1D, 250, 850, 90, Kiss X10, M6, Ra, Rebel SL3, Rebel T100, Rebel T7+, Rebel T8i

I have 3 550EX and 1 580EX for photo table setup with Harbor Digital Diffuser on each unit. This trigger works quite well with 1DS Mark-2 and flash setup I have. I don't have any AF cover fall off issue. And the hot shoe mount works quite good with a locking pin. It doesn't have a knob that you can tighten the unit on the camera but the unit is very light, and there's enough friction between the hot shoe and the trigger mount, so you don't really need to tighten it. I haven't tried long distance setup in the field as I use this for mostly product shot on the table. But it handles most indoor family gathering shots with no problem. It uses a special battery but it is readily available in many places where common batteries are sold. I always have an extra battery in the bag for just in case. This is an indispensable tool for my need and it is very reliable.

I use mine to trigger three 430EXs. I've no complaints, performance wise, that are not inherent to optical triggering. (Although a native Canon RF based wireless solution would be AWESOME!) I also use it as a focus assist when taking lower light natural light pics. It'll make a lens that likes to hunt snap to as if it were plenty bright. (Makes my Canon EF 50mm f/1.8 II seem like a much better lens.) The only real complaint I've got is that it has no battery life indicator, it just dies, and it takes a somewhat unusual battery. (Why not AA or AAA?)