There are plenty of people who travel from West Lothian to the airport. At £4 ish each way it is far cheaper than a taxi or other public transport. There must be some demand or the 902 would be finished already.
I wonder if it will pick up some local traffic too. Cheaper and quicker to Broxburn than the 72 and seems to be mostly timed in between their journeys.
It reminds me of the Horsburgh 777 nearly 20 years ago:
https://web.archive.org/web/20080313234133/http://www.horsburghcoaches.com/service_routes/777.htm
That was an hourly circular and served all stops (IIRC), Ember is doing an equivalent 40 min headway.
It's an extra £1.40 on the fare to travel from Ingliston to the Airport. I wonder if that's some indication of the airport passenger fee.