Just looking at this and it seems pretty good. Has anyone used it or got an informed opinion? Their data roaming prices look really good, although the initial setup costs NZD$31.44 (at todays exchange rate). Their highest per MB roaming price is around $1.43.
About the only time I could see it being a benefit is when you are travelling through europe, and either don't have time to buy a sim in each country, or won't be there long enough to get any value from the local SIM's data allowance/credit.
Probably only worth doing when you have very low data use expectations.