I am lucky I can dry my clothes on the clothes line about 6 months of the year. In the winter, I only put sheets and towels through the dryer, I hang everything else up in my laundry room.
When I first saw ventless dryer, all I could think is humidity, but then I realized that I am adding to the humidity in my home by hanging clothes to dry inside, but not increasing the heat. I do not have humidity issues, so it is not a problem.
Then I realized that my cousin in NZ has a dryer that does not vent outside, but it does vent through the door into the room. It is not an issue for her as her laundry is in a separate wash house, not attached the her home. Plus all my family in NZ use their clothes lines almost exclusively, electricity is expensive.
It is interesting how laundry facilities vary around the world. When I think about my NZ family all but one have their laundry/wash house either outside in another building, or built onto the exterior of their house. When my Kiwi Grandmother moved to Canada and eventually built a house, she did the same thing, she put her laundry in an enclosed porch. Luckily we are in a part of Canada where it does not get too cold and we do not have to worry about frozen pipes.