Every so often a 'GAK - any good?' thread pops up, and the posts are pretty consistent - lots of 'yes, I bought from them, all good' replies, and a few 2nd- or 3rd-hand reports of problems. I fall into the first category.
As planer mentioned above, they are a proper shop, not just a massive warehouse full of boxes (although I guess they must have one of those too). If you are ever in Brighton, I strongly encourage you to go for a browse. I spent 10 minutes gazing slack-jawed at the new and used pedals in one of the windows, before I even went in!
You can't miss the shop, it looks like this: