I didn't get the email, so just phoned to see if it was for selected subscribers or anyone on Pay Monthly. I'm told the latter. An extra 200 MB of data's a pretty good anti-churn measure, and of course you can still put that SIM on shared data for when you run out of the 200 MB.
To grab the deal, you have to visit a 2Degrees Store with proof of being on Pay Monthly.
Nice one 2D. I'll be snapping one up to put in the iPad Mini.