These adverts do not stay up very long in my experience.
I only ever went to a vivastreet advertised working girl once and that was because of a review. Even if you take one for the team - the information will only be useful to the rest of us for a couple of weeks at most.
However, many of these girls are very hot, and can often make up for a vanilla service. I overlook the lack of OWO if the girl is really hot, because well hotness makes up for a lot of things,
If you really fancy a girl (cos thats really the only reason to book imo), book a half hour only and be prepared to walk if it isn't the girl. I don't know that anyone else will say anything more really.