The lantern is on during the light cycle, yes. I am using a fan which ocillates across the plants, and generally disperses the CO2 falling from the lantern. The lantern is off during dark cycle. I read that it only needs the CO2 during the light cycle anyway.
During summer I was venting out of the room to the outside. This should not affect the CO2 because the way I am set up the venting is on the opposite side of the plants from the CO2. Besides, I have moved the monitor around the room to experiment and the way I am blowing air around in the room, it is quite consistent throughout the room.
It's just so easy...no muss no fuss. No buying dry ice, propane is lasting a long time. I just turn the knob and light it, make an adjustment an hour later, and voila it is generally set for the day. I do turn it off if I leave the house, but it seems quite safe.
It may not be ideal for every situation but it sure seems to be for mine.