I never use the humidifier. CPAP humidifiers are designed to prevent the nasal passages from drying. They don't do much for the mouth. Anyway, I rarely mouth-breath at night, so any humidity from a humidifier would not enter the oral cavity.
General Discussion on any topic relating to CPAP and/or Sleep Apnea.
Personally, I find the "i" models less likely to leak because the hose connection is on the top of the user's head. When the hose connection is on the front of the mask, the hose can pull on the mask and break the seal as you change positions while sleeping.