The GSF in Worthing (nr Brighton) is spot on. I have my inside man, so where i dont feel that OEM quality is necessary, i give him a shout and get a good price..! GSF are, what they are, out to supply affordable parts to the public and trade alike. The prices are near rock bottom on almost everything, so as expected the quality reflects this with some of the parts, although i have found that some are pretty good as well..Beggers cant be choosers!
As for the G brakes, i cant say that i had a great deal of experience with them, but i do know that as satndard they aren't that great, still mine probably needed a good servicing! One thing i can confirm is that they are miles better than the VWI (GT..etc) brakes which are the pinicle of pointless!!