I own 3 Flashes (1x Canon Speedlite 580EX II flash and 2x Canon Speedlite 430EX II flash unit) I (ST-E2 Speedlite IR transmitter remote flash trigger for 550 / 420EX Canon) use together with a remote flash trigger. By the way, I use also like umbrellas, these are cheap and easy to transport and clamped quickly. But a softbox is there already a lot better, it can be soft and it is easier to control / directed facilitating targeted lighting.
That is why I have now overcome this to create the Flsh2Softbox system. With overcoming, I also believe that you have to ignore the price of my opinion is simply much too expensive. Another negative drawback is the flash bracket when the slide Unfortunately no ramp for the out standing flash contacts on the flash. So you have to push when inserting the bolts with a fingernail contacts easily or press a little harder. Anyone who wants to afford that, can better flash bracket as the Hama hot shoe with insulating this I can recommend.
For the adapter you still needed a robust Neiger, here I can Manfrotto Lite-Tite Umbrella Holder recommend 026. This is very robust made (No plastic toys) and still holds a umbrella holder and 2 spigots which can be screwed into the adapter a.
The adapter itself is robust produced, but in only 3 parts which make it up, is not difficult. I use currently 2 adapter I use this with a 60x90cm softbox and a 95cm Octobox, both of sambesigroup.com. With this combination, I drove very well so far and I would buy again at any time.
Despite the adapter can this really be useful, I'll only awarded 4 stars. Reason for this is the expensive price and a bit more because of the flash bracket, but that's really just a small flaw.