I think they would be illegal, although they could get around with a loop hole if they sold the hardware with default factory OS/firmware and supplied a link to obtain the "upgrade" software.

Are they shipped from the UK or are they coming from China/HK? That would instantly flag it up for me as very dodgy.

Looking at your link, and similar links these are all feeling like Chinese copies using Android KitKat 4.4 OS. As soon as the first TV boxes using Android were legally released I'm sure they got to work cloning the hardware. After all it must basically be the same phone components they manufacture over there anyway, and Android is free. So all it then needed was the unlock codes cracked so unlock the paid for apps installed under Android.