I don't think this is as good as everyone thinks.... you're missing half the charges.
First of all, when you load the card you are charged 4.95% commission.
Second, because you're using your Euro based credit card, to make a STG payment, your credit card company will charge your a charge. MBNA charge over 2%. I'm pretty sure the correct figure for MBNA is 2.75% (Could be 2.5% but I'm not reading the small print again!)
Third, if you look at the fees for EntroPay they say that they charge you 2% for payments in a different currency to the card. So when you purchase flights from RyanAir in Euro on your STG Electron Card, you are paying a further 2% in charges.
So that's 4.95% +2.75% +2% = 9.7% But worse that that, you're paying % on percent.
Therefore your flights are costing almost 10% extra. Now if your flight cost €50, you're end up paying almost €55 after charges.
Follow me though on this one.
Lets suppose your flight cost €50 with RyanAir.
In order to make this payment with your STG card Entropay will require a 2% foreign currency commission, which means that you must have the STG equilivant of €50+2% (€51) available on your Electron card.
In order to get the Stg equilivant of €51 onto your Electron card, you must transfer €51 plus their commission of 4.95% (€2.52) which means your total transfer must be €53.52.
Not to transfer €53.52 worth of stg from your own credit card, your own credit card company will charge you a foreign exchange commission of 2.75% which means that you actually pay €54.59! And that assums tha that the exchange rate hasn't moved while you make these transactions.
It would still work great for the low cost flights, but not very well for the higher cost ones. If the flight was over €100, you'd certainly be better off paying the credit card charge!
So for me, I'm still looking for another solution before my MBNA gift card balance runs out...