You only need one card-reader.

The card-readers are all the same bar the branding.

So if you bank with Barclays, NatWest, Nationwide, RBS and no doubt others too, you can get away with only carrying one card-reader around with you.

I’ve tried it with a couple of the major banks and building societies and I can confirm that all cards and card readers are compatible.

They’re using the APAC – UK payments association – standard. There’s some background on this slightly out of date page on the APACs website

It’s still a pain to have to carry one around though. Puts a terrible bulge in the pocket!