I have one of these machines. I reckon it does a good job. As for how long the effect lasts, it really depends on if, for instance, the car belongs to a smoker. I do one vehicle that is used for stable runs. The owner has me fog the car every 4 to 6 weeks. I charge £20 a time. She suffers from a few allergies and tells me thay are much better since I started treating her car. The fogger on ebay is a bargain if you get it at that price.