The Fragramatics hose assembly works great on the Doyle units.
I prefer to keep the push-button working because of the mess it makes when people hang up the hose with the unit still running; it's also a lot easier for them to control where they spray. I keep a couple spares on hand (You can get them from Home Depot for $3) and change one maybe once a year.
I've been ordering all the components for a fragrance gun minus the outer hose and use a fiber-wrapped pressure washer hose to assemble my own. They last much longer and are less prone to kinking than the stuff Fragramatics uses. I use blue non-marking hose.