The 600 was limited stop and confused users. It may of changed towards the end of of its short life span. There was also the First 601 which was limited stop too.You would have thought a Lanarkshire to Airport type coach service would have been better doing Wishaw/Motherwell - Hamilton - East Kilbride - Newton Mearns - Barrhead - Paisley - Airport. Now that the Glasgow Southern Orbital exists for the EK to Mearns bit, and the new road is open for the Mearns to Barrhead jump, there would be no need to go near M74/M8/City at all? Is that not more appealing to customers? Direct link for 6/7 towns straight into the airport.
Did Arriva's 600 stop at every lamppost from EK, Busby, Clarkston, Thornliebank, Silverburn, Paisley and then onto Glasgow Airport? If so no wonder it didn't appeal.
I do wonder if the 903 is a bit AI-involved. Given all the postcode data of airport passengers over a period of X months, this is what AI thinks is the best service to pick off the most postcodes... but to my untrained eye looks like two services mashed together: Airport to SEC Campus/Glasgow Central and Airport to Lanarkshire (or bits of). Could have been a Citylink liveried bus doing the former and the West Coast Motors vehicles doing the latter.
Yes, seems like a computer generated route but heck what do we know. I also thought it was a feeder to get the coach to do the 903 to Edinburgh Airport but I don't think so.