Viva st is ok as long as you use a different number I've had some lovely clines from Viva st
It always pays for itself
I have never actually lost money from VS, but the handful of clients I did get were pretty grim. I think two of them were scary (one tried to steal the money back, the other demanded his money back and I had a hard time getting him out) and I think there were maybe one or two others I've seen and didn't enjoy.
It may be different in London, though. That said, my friend used VS when in London a couple of weeks ago and none of the callers were people she'd like to see. In her words, "foreigners asking for bareback and/or haggling."
I think I may have thinner skin than you (no disrespect meant to you in any way, Paris - I think you manage these guys very well and keep them in line) and I am more easily unsettled if I go outside my comfort zone.