Caffe Nero seem to be very generous with the freebies through the app.
I found out the hard way it's best not to use the app in the same transaction as the O2 Priority freebie on a Tuesday though. This week I bought a hot choc on the O2 app (free) then bought my friend a coffee on the Nero app which should also have been free as I had one stored on there. But instead it gave me the hot choc for free again and charged me for the coffee.
Something similar happened before where it combined freebies. However it wasn't worth holding up the queue to complain as I was instantly awarded yet another free drink for next time for filling up a loyalty card as they gave me 5 extra stamps on it. So with the Metro one too (thanks again
@The Reverend ) and a couple of full "old school" cards I found at home, and O2 Priority day again on Tues, I'm ok for coffee for a few days