Tesco or the PO for currency

Any one used the online currency acquisition service offered by Tesco or the PO? Are they reliable, for example do they deliver next day as they say?
They both seem to offer the best exchange at the moment, albeit that Tesco is very slightly higher at 1.5384 (compare that to 1.43 offered by Travelex at Heathrow last week, significantly better and I'll only ever use Travelex now in an emergency!).
They both seem to offer the best exchange at the moment, albeit that Tesco is very slightly higher at 1.5384 (compare that to 1.43 offered by Travelex at Heathrow last week, significantly better and I'll only ever use Travelex now in an emergency!).