Contactless payments don't need PIN (up to some small but comfortable amount) and go through almost instantly.
So 70% of the time it saves time and 30% of the time it wastes time. Then I broke my phone and bought a replacement without NFC so I don't have the option anymore anyways.
It's a great system, however, I think the kinks need to be worked out a little.
(I had a Nexus 5x FYI)
That seems an easy way to get your merchant account cancelled very, very quickly.
Even if it did, the bank is likely to block the transaction, or call/text for verification.
I heard that those are very easy to crack. It might have been this article from 2011 where I read about this (German, sorry): http://www.zeit.de/2011/21/Kreditkarten-Sicherheit