It's always difficult to use Companies you haven't used before and there are many that like to play safe.
We always use Transfer Wise now, but the first time was a tad worrying, especially as it was a highish 4 figure sum. I can't guarantee any business but it works for us and quick getting money to our Greek Bank.
Their exchange today still hovers around e554 for £550 pounds , after commission which on this sum comes in at £3.60. The website also shows a comparison list against Banks.
Cheers
Negg