I have never seen one or indeed seen one in action.
I have never seen any scientific studies to suggest that salt therapy helps in COPD (Chronic Obstructive Pulmonary Disease)
Should salt inhaled into the lungs? Yes, in my experience salt is a mucolytic agent ( helps to break up mucous ) and salt solutions were used to drip into tracheostomy patients to break up the phlegm and ease breathing.
So yes, give it a try as it will do no harm.
Remember it should be used as complimentary to scientific drug therapy...steroids and bronchodilaters. ....not instead of.