I have been using them for a while but the design sucks as they are too high and unstable. I decided to mod them as I use SB-80's and they have a PC sync socket so I decided to try adding pc sync cables to them and what you know it works!  I now Velcro the the receivers  to the head of my flash and use the sb's much more stable foot on the cold shoe of my brolly holders.
Before they sat too high to properly hit the centre of the brollies now they are perfect Can post details of the mod if anyone is interested but its really simple and probably obvious.
I also fitted a mono jack off an old guitar lead to one receiver to turn it into a studio trigger which also worked.

I just bungee / velco the flashgun to the shaft of the umbrella - the light hits the brolly more or less dead centre - I don't trust the radio receiver hotshoe fittings and it also lifts the flash too high.