What's the difference between the Inkbird ITC-306 and ITC-308?

According to discussions on r/Aquariums, the 308 has one heating outlet and one cooling outlet (useful if you also run a fan or chiller), while the 306 has two heating outlets and is built around dual-probe redundancy. Reefers and homebrewers tend to prefer the 308 family; freshwater keepers running two heaters often prefer the 306.