Not going to risk it

Slow and clunky to set up personal details.
No indication whether the app supports non-UK telephone numbers. If so, the app gives no instructions how enter them. There is no ability to enter the + sign to indicate an overseas number.
I decided I wasnt going to turn the risk of being charged for a ticket only to have it disappear into the void, so I gave up on it.

Jung-sin about Heathrow Express, v1.4