Globalgig sounded almost too good to be true. Last time I looked, the prices weren't available. Now they are. The cheapest offer is £20 a month for 1GB on a 12-month contract. If you cancel early, you pay the missing months anyway.
My UK Giffgaff Gigabag is £7.50 for 1GB a month and I can cancel at any time.
When I was in Italy last year I paid €10 for a SIM with 1GB, valid for (I think) 3 months.
In Germany, Blau.de offer 1GB a month for €9.90 or 3GB for €14.90.
Apart from the convenience of not needing to swap SIM, I don't see a lot of benefit in the Globalgig option unless there's a need for it to work in several different countries in quick succession.