Well Madeira is part of Portugal and the Canaries are part of Spain so both technically in the E.U. but yes bringing back duty free is still attractive if you shop around and your personal allowances are much higher than those in a non E.U. country.
It i the same as coming back to the UK direct from the canaries you will have to pay excise duty to hm customs as the canaries are exempt EU tax and you will have to pay that tax when you take tax free goods into a normal EU state.
Been on this cruise and we flew to Tenerife and returned to the uk from Tenerife your duty free allowance is 200 cigs or 50 cigars, 2 litres of wine, 60cc perfume and £145 wort of gifts. I have taken this info of my cruise news letter I received on the ship. Hope this helps.