It makes sense to use a single-action airbrush to paint larger areas. But I am not sure about spending another $200 plus for the Iwata Custom TR.
Is it the single action or the pistol trigger that made the biggest difference?
The Badger 200G can be had for 1/3 of the price of the Custom TR, but the cup is smallish and the trigger is push down. Airbrush-Depot Master brand has a number of pistol trigger, single action airbrushs for under $100 too, such as the Master G76.