If you do pay in pounds, the merchant will charge you to convert the local currency into sterling and then charge you again to convert back to the local currency.
In the extreme, Cyprus could exit the Eurozone, convert over to a new currency and then Cyprian bank depositors, Cyprian creditors and the Cyprian people en masse will all be trashed when the Cyprian government devalues the new currency.
This meant that countries holding USDs as reserve currency were under increasing pressure to convert their USDs into gold to protect their own positions.
Savings from not having to convert profits earned in different European currencies or to hedge against currency fluctuations amount to more than 10% of De Kuyper's annual profits.