I have just received mine (bought on Ebay, shipping from China took 6 days). Haven't used it for any proper shots yet, but since I have read comment that the Flashdisc loses quite a bit of light, I though I would do a comparison.
I just took pics of my desk, using the flashdisc, a flashbender (with diffuser panel) and an Eazybox type small softbox. Flash with diffuser on camera set to manual, 1/4 power.
Comparing in Lightroom, the shot with the Eazybox was by far the brightest. Second was the flashbender, which needed its brightness boosted by 0.75-1 to become similar to the Eazybox shot. The Flashdisc was by far the darkest, and needed boosting by 1.5-2 to get to the same brightness as the Easybox.
The quality of light, at least in this simplistic test, was very similar for all three.
So the convenience of a diffuser that folds up very small, compared to the others, is paid for by losing an extra 1 or 2 stops of light.