What does it protect the car from? I mean, it's already in a garage. I guess it filters the air, but it also constantly blows air on the car. If there is some dust in the air in the garage normally, I suppose it would be filtered, but I doubt dust will hurt your car. It would just settle harmlessly on the car. If the air in the garage is stale, I don't think a filter can make it fresh. Filters also don't remove humidity.
That part where the bag is not inflated would concern me a little too. Although if you carefully laid it over the car, it might not drag while it lifts.
I'm just not sure what it's supposed to accomplish. What problem does it solve? It won't stop tires from flat-spotting, or fluids from degrading, or metal from binding or rusting. Aren't these the long-term storage problems more so than dust?