I assume you mean this report:
http://www.glasgowairport.com/media/37884/ga-exec-summary_final.pdf
I'm a closet fan of PRT generally I must admit, but for such a point to point link I would have thought a shuttle system based on larger vehicles than the standard 4 person Ultra pod would be more appropriate. The report claims the need for interchange would be off putting and that would limit modal shift and the system would require 'subsidy'. I would argue that operational costs should be considered no different to those of interterminal links, moving walkways, or even elevators within the airport premises, ie an intrinsic part of the people moving infrastructure of the airport itself. To mitigate the interchange disbenefit, the entrance at Gilmour street could be considered, signed and branded as an entrance to the airport itself, so instead of catching a shuttle to the airport, entering the shuttle terminal would be seen as entering the airport itself, albeit a peripheral 'portal'. Gilmour Street station, being so central, would also form a fantastic link between airport and the town itself including all its local bus transport services. Rail services to Ayrshire and beyond as well as Glasgow would also be linked in far more effectively. I would argue if designed well a free on demand 24/7 airport shuttle from Gilmour Street could result in the maximum modal shift from personal car both within the local area and from the wider region, and for airport employees as well as passengers.