We also have the ionic from Sharper image...quatro model , I think. It works very well IMHO, DS has not needed any meds for 8 mo's.....this is huge! It is extremely quiet, but kinda pricey...about $350. My Mom bought it for DS, she investigated it and wanted to help him out. What a Grandma!
Good luck in your search. Asthma can be sooooo tricky!