I've never bought one, but I have read reviews on backpacking sights from knowledgeable people. I think you can get a heck of a deal but the quality will be low and it will be designed by someone who does not have experience backpacking. The biggest complaints are they don't meet the rated temperature (expected) and they tend to be built for an average Chinese sized person. They can be a really tight fit for the average American sized person. If you are shorter with a slighter build they could work for you. The last complaint I hear is they tend to include extra stuff that isn't necessary. They also probably won't be differentially stuffed. They will have the same amount of down under you as on top, which will make them heavy for the actual temperature rating.

I wouldn't be turned off by duck down. Enlightened Equipment does some amazing stuff with duck down.