When they arrived they were all 13.0 grams +/- .05 grams, the variance in weight between the props was minimal and the quality difference appeared noticeable to me.
All four were in balance though I did add a 1cm square of cellophane tape to one blade but this is considerably less than the stock UPair blades that came with the quad.
I had over 80 successful flights on the last set of stock props and they would have lasted longer had not I rearranged my driveway with them. Hopefully I'll get as much life out of these DJI props. I ordered another set of these sames props today. It looks like a great buy at $13 for four of these.
Update: June 18th - I think that the noticeable improvement in quality of these props is what convinced me, without actually seeing one, that the DJI Phantom series was a quality build. Now, actually owning one, I'm very glad to have purchased one. The Phantom 3 Professional is an incredible machine!