Until now I've flown my quadcopter with plastic 5" propellers from Gemfan (5030 to be precise). They were the cheapest and most readily available in Switzerland. My quadcopter is small, but it also fits 6" props. However the Gemfan 6030 plastic props would often break apart where the blade connects with the shaft. Even mid-flight while hovering. I suspect either a material weakness or a manufacturing defect. Or maybe I got a bad batch. In any case, it made me cautious and I've avoided flying high or fast due to the omnipresent danger of crashing. Here is is a pair of the 6" props each with one blade broken away.
Now that I can fly reasonably well don't crash nearly as often as at the beginning, I looked into getting carbon props. Carbon is much stiffer than plastic, which yields much better performance. And I could also try 6" again. Carbon props are created as a single continuous piece, and therefore they don't have a weak spot like the plastic props.
On my quadcopter I have motors from T-MOTOR, the same company also sells carbon props. But they are expensive and difficult to buy in Switzerland. I looked at other shops online and found a seller from China on ebay.
The props were cheap, less than a third of the price of T-MOTOR props. And shipping was free. I knew that I would not be getting the same quality as from an established manufacturer. But still, what I saw when I opened the package was a slight disappointment.
Notice how the edges are uneven and frayed. And the drill must have been very dull by the looks of the center hole. Also, I haven't tested yet how well balanced they are. I won't be surprised if not at all.
I don't think the props are necessarily bad, I'm confident that they will perform equally well as brand-name props. Here are some closeups of the props mounted on my quadcopter.