When /if I move to the city I'll consider them.
It's a quick way to reach tourists.
I used to own an interesting book on the subject:
Tart Cards: London's Illicit Advertising Art(http://ecx.images-amazon.com/images/I/51FVV2SSE2L._SL500_AA300_.jpg)
Downsides. Illegal since 1984 IIRC.
There was a one year break where it was legal.
Due to privatisation of BT
or split of BT from the Post Office. I can't remember which.
It took a while for legislation to get updated.
Councils regularly request the police to take actions to reduce the incidents of Carding.
AnecdotalThe biggest problem is this.
I have heard that use of Tart Cards is more often done by escorts
with no legal right to work in the UK,or possibly even be here in the UK.
Police with intelligence from uk border agency raid premises
where they suspect "Illegal's" are escorting.
If the raid produces no results or less than expected,
the police team will use these cards to go on a fishing trip.
If you are legal in the UK for escorting, then there is no legal problem.
It's just that a police raid can ruin your day.
Even if they say sorry and smile when leaving.
Apparently escorts advertising 'Duos' get swept up in the same approach.