I've been using one of the cheap Chinese knock-offs for a year or so and am very happy with the results (these don't seem to be available anymore on eBay???).
I've used it on an AF-500FTZ, a AF280T and Promaster 7500EDF (had to slightly modify it to fit on the Pro), indoors and out, and the results are very consistant - nice even lighting with no harsh shadows. On all the flashes I use it in the straight-up position.
One modification I did was to tape aluminum foil around the back side so I didn't get so much flash in MY eyes. All in all - thumbs up!!