Thanks for posting that information on the Cactus units. I'm not familiar with those ones, but earlier this year I made a spur-of-the-moment decision to purchase a used
Fotodiox Radio Slave Kit for about a quarter the price of a new one.
OK, so I haven't got to use this caving yet - and it's certainly not going to be water/mud proof, and perhaps not so rugged because it's really designed for studio work. Plus it's the "budget" brand so I'm not expecting too much. But what the hey, the price was right! I like the idea of an RF option because I get frustrated when my nice, sensitive Gibson slave triggers are regularly triggered by fancy PWM regulated LED headlamps (including my own). I'm not sure the range will be as good as my Gibson units, especially non line-of-sight, but when circumstances permit I hope to be able to play with them a little more and find out.