Things are not quite that simple.
I bought 10 cartons of cigarettes at Maria's, using my Clarity card. The cost was €312.
If I had used cash at the rate I bought it, this would have cost £250.60 - but Maria charges 3.5% for credit cards, so the actual cost on my statement was £255.83.
Without the additional interest I would have paid £247.60 - in which case Clarity would have won. So, clearly, next time I will pay in cash!
Yes, I know Maria charges commission on credit cards but it is 2% not 3.5%.
Even with a 2% commission I still got a reasonable exchange rate in Peli & Maria's shop (I also bought tobacco, not for me), couldn't resist her smile.
My purchase at Peli & Maria's was 1.26 minus 2% = 1.23 (which is better than the exchange rate in Ag Stef, after they've taken 2% commission)
As you probably know I was getting 1.26 on the majority of my purchases (tavernas mainly) using "no commission credit cards"
Revise your sums again Jimbo, using the correct commission of 2% I think you'll find that the Halifax Clarity Card was still better than paying cash at the rate you bought it in the UK (1.21 as I remember)
I suspect you didn't use the Clarity card much as you were staying at the Nafsika on half board but if ever go b&b it will serve you well when you eat out.
I've always found that it's best to use these cards only in places that do not charge commission and never in an ATM. Of course we all know that a few tavernas don't accept credit cards.
The other alternative for you Jimbo is to give up the "weed" then you can save shed loads, no, let's not start that one again!