I have mine in a fish tank with plastic netting on top - that's good for ventilation, although if I could give them more I would, and it helps with the bonking as it have it slightly slack. I have some others in a basic hamster cage (plastic bottom and wire walls and roof) and they smell less (there's also less if they though) and I have a cereal box cable tied to the wire on the top - it's was a temporary fix, but it's worked for now.
I'm yet to find a substrate I like, and that may be the key to really keeping them fresh! Something absorbent that can be spot cleaned regularly.
I do find them quite dusty, so if you have asthma or anything you might want to reconsider. I'm not sure how they compare to other birds though.