Do you tether/does your contract allow tethering?
On the other hand, Three usually allows tethering in the home country of the contract, and also offers contracts on mobile broadband devices.
Three Ireland currently don't do this for Three Ireland accounts, though tethering is prohibited on All You Can Eat by policy, not by network infra.
In the end I just got a local Three SIM, I think it was ~£6 for 700mb. Trying to find free wifi (without 30 minute access restrictions) in Hong Kong was impossible...
All I can say is that I've been to the UK and used my laptop with no issues and that I'll try in Spain in a couple of months.
Anyway, you are much more informed than me in this area, so I'll shut up now :)