Just queried it with Grumpy and double checked - it is illegal to have such devices in Portugal. Should we be found out - and although they're slow, they're sure - we would then not be able to have ANY internet connection and even a mobile phone would be dodgy. For ever.
We'll wait and see, it's not a major thing for us.
As an aside, the laws here might seem a bit weird, but if you're caught having an English car here, after 6 months and you're still not registered, they'll confiscate the car and escort you to the nearest border