In message , at
00:12:30 on Thu, 31 Oct 2013, Neil Williams
remarked:
Would this cause problems?

Yes, because the readers are being modified to accept these as a pseudo
Oyster.

I think presenting two different cards always caused a problem. It's the
Achilles Heel of virtually every RFID card implementation.

On the other hand, my dual "Paywave and Oyster" Barclaycard works fine,
which means perhaps it's got some clever avoidance technology.

--
Roland Perry