I purchased these batteries (the gold ones) back when I had a GS2. They, like these quoted about 30% higher mAh rating than the OEM batteries. My experience was they lasted about the same as the OEM. I think they just fudge the numbers for marketing purposes. The batteries are certainly cheaply made, I had the top terminal plates come loose on two of the ones I owned. When I bought them they did not have NFC support like the OEM battery, but they made no claim for it either. I used them for about 2 or three years with no real issues other than the terminal plates which was fixed with a bit of tape.
If you need a cheap battery to back up your existing batteries I would say they do the job. If you are looking for a higher capacity battery look elsewhere.