The problem with "AGM setting" on chargers is that voltage is usually /always lower than the Flooded voltage setting.
AGMs have charging specs all over the map, so a low voltage setting could undercharge a particular AGM. You have to know the actual specs for your AGMs to get it right.
Then you need a charger that can meet those specs. EG, Lifeline wants 14.4v at 77F, but my AGMs specify 14.5 to 14.9 so with them I would use the Flooded setting with a non-adjustable voltage charger.
BTW Go-Power was sold to an outfit in California recently, so they might have changed their ways. They used to be expensive compared with other similar products, which can't be good for business.