I have also had really good experiences with Sebastien Grey, at the office here in NYC. They actually just changed to a new office down in flatiron, which is a lot nicer than the old one. I bought my first suit using the gilt voucher, and it was great. Ended up getting a second, and actually pulled the trigger on the end of year deal for two more. I have only worked with one salesperson thus far, but she has been great, and fit was pretty much spot on. And then reordering has obviously been simple and results have been consistent.
As for quality, they are good. For the price, probably one of the best values you can find. The gilt deal for less than $600 actually includes full canvas construction. As mentioned previously, the suits I have received thus far have been made in china, so there is that. But as I said, all in all, I have had a good experience with them. BTW, I have tried two other custom suit places that have offered deals, and Sebastien Grey is by far the best of them.