Budget Travel - Ryanair & their gift vouchers & CC fee

Did any of you ever bought the Ryanair voucher? The thing I wanna know, is the credit card fee when you buy these vouchers, it is said that there is no Visa/MC fee but I never trust them - what is the truth?

No fee but if you use a voucher for a flight then you lose any remaining value on that voucher - so if you book a £10 flight with a £25 voucher you lose £15

Yeah, I know that. But my purpose is, when I buy a ticket with higher value, to buy a voucher and pay with CC (and get miles on Citi-LH-card or 1% cashback on the other card), the rest with Visa Electron card (to ommit the fee).