People used to highly recommend (and had good experience with) another similar outfit - until they went bust and took all the outstanding money with them. Is "your" money 100% secure in some way? Check. Only deal if it is.
Or better still, use a fee-free credit card instead. No risk (except of exchange rate dips - but then they could just as easily rise.....)
This is my concern and we need £3k changing. Anyway I've now found some currency exchange websites for where we're going which are showing slightly better rates so will take cash/TC and change while we're there.