I live in London so I have no idea what are the good and bad areas of Birmingham, but if the area has a dodgy reputation (deserved or not) I think it definitely has an effect on business. I would much rather punt late at night in Kensington than some of the dodgier areas of London, no doubt about it. I believe that the flat they work from may have some kind of rota of girls from week to week or month to month, but I have only been there once and don't know much about that group that they seem to be part of (Divas?). They looked at coming to London but couldn't find a suitable apartment, I guess it may be that the prices are that much higher, and they may be worried about the profit margin, as I think they charge the same prices in Brum and here.
Anyway good luck if you meet them, the reviews on here seem to be mainly positive but a few neutral and negative comments have been made as well, I absolutely love meeting them but it's all a bit subjective.