Interesting to see FreedomPop moving into the international data market. As a reader of a US deals forum, I'll state that their free service offerings in the US come with very mixed reviews, with people reporting that their credit cards have shown random charges for supposedly free service (you have to have a credit card on file with them). This may just be a matter of people not reading the fine print, unchecking the right boxes, etc., but I think a "proceed with caution" warning should still apply. Perhaps pay for the SIM with a prepaid credit card and keep that on file with them.
Given that, I'd be much more inclined to try one of Three UK's SIM cards, but since I'm never in the UK, I have a feeling that sooner or later my service would be cut off as per the aforementioned terms and conditions.
Note: Doing some research on the FreedomPop service,
here's a page which shows the list of countries being added "soon" (this year?). The list includes:
Bangladesh
Brazil
Hong Kong
India
Indonesia
Malaysia
Mexico
Philippines
Russia
Singapore
South Africa
Thailand
Vietnam
These will be in addition to their currently supported countries which are basically the US and most of Europe (missing some of the eastern European and Baltic states).