I have 8-9 garments from GB. Very happy with these. You do however need to be firm with them; sometimes they do stuff on their own initiative that I don't like. As an example, they made two sports coats for me with roped shoulders (roped shoulders look like crap on me because I’m very tall). They were happy to fix this though. But still, it just shows that you need to be firm. Here are a couple of pointers that might be useful when you deal with GB:
A) Be firm and make sure that they know exactly what you expect, and make sure they write down the exact construction you would like. They do so many different types of styles now and they don't have a house cut per se so make sure you are exact otherwise you may end up with something you don't like.
B) You should be somewhat experienced in MTO and/or bespoke making in order to be able to provide precise instructions. Also, be firm if there is something you do not like with the ready garment, if it does not fit 100% make them change it. Don’t accept that it looks “ok”.
Still, it’s not Savile Row, and you’re paying £1000 and not £3500 for a suit, so some things you do have to expect not to be on the same level, of course. If you want a perfect bespoke experience, you should go to AW Bauer or some other high end bespoke tailor.