The difference is that Travelex is actually a service people want in airports (which is why it is also even available in some lounges). Dixons and Dior are not.

I've also found that Travelex have a pretty good customer service ethos. They found time to call me on August 10 2006 when I had a currency order due for collection to find out what I wanted done with it - I don't suppose many other travel companies called all affected customers personally that day. They've also handled various other problems very smoothly.