I'm not sure about the overclocking guarantee, but I am really happy with the service from GP32z. It came quickly, and when I got it, the shoulder buttons were not that great (which is a pretty common issue with the BLUs, I guess) I asked if I could get a button tune up kit since it was a defect in the first place, and he pointed me to Azure's thread when he had the same problem. I was halfway done fixing it, then a friend came over and I let it be for the time being. In the meantime, he even sent me a PM checking up on me to make sure I had it working. I did a little later, and I don't think that a button tune-up kit would have even fixed it.