There Three broadband is excellent WHERE IT WORKS. You avoid the expensive data charges, as you're on a flat fee.
The downside is that it only works in a handful of countries (which does not include France...most likely destination for UK pilots). If you are outside a partner country, then it simply does not work at all, at any price.
From memory the countries that it works in are UK, Ireland, Austria, Italy, Sweeden. Then it also works in Hong Kong & Australia if you are on contract, but not prepay.
Outside the list of supported countries, then you have no data access.
dp