I'm after some advice, my Son (16) is about to head off on a school trip, spending 6 days in Spain and then another 7 in London. Wondering what the best option is for getting him connected.  He is currently with 2degrees, and while they do have intentional plan, they only have small data allowances.  Doing a quick Google seach, I see the likes of GiffGaff where you can get 40Gb of data and unlimited calls/txt that will work in both Spain and London for 20pound, (they also have addons for international calls/txt).  They will even send out the sim before he goes. 

So, from seasoned travelers, is it worth getting a local sim, or just do international roaming?