Newirishman sums it up well. Most of these boxes themselves are not illegal, using them to view free-to-air broadcast channels is also perfectly fine. So if you cancel your Sky subscription, you will still receive all the free-to-air channels, and that's perfectly fine. The Broadcasting Act is really clear, I don't understand how further links would be required to show that cracking the encryption on a subscription channel and watching it without paying for it is not OK.
The piece where you're paying the providers of that box for a 'subscription' to their illegal hacking service is, obviously illegal, and the modified box they are selling which is capable of carrying out the decryption of subscription channels is also illegal. Why else would they be so cautious, only putting some of the pertinent information on Facebook, hiding their website behind an offshore privacy service so the Irish authorities can't trace it, and then not even credit cards or PayPal for payment?
It's simply not possible to legally receive all the Sky channels including movies and sports and even the pay-per-view movies for anything like €80 a year.