If you're buying an Inogen then buy directly from Inogen. If you're buying a Caire then buy from The Oxygen Concentrator Store (that is where Caire, Inc. directs its customers). Do not buy from 1st Class Medical. The first machine they sent me was dirty and the motor stopped working and the alarm went off within the first 1/2 hour. Sent that back. The replacement machine worked, but they did not fulfill the purchase of the external charger plus neither the carrying case nor backpack fit the machine, all of which I needed to travel. Had to return machine, but they kept $90 in shipping fees for the first broken machine, $90 for the return of the unfulfilled 2nd machine and an additional $99 restocking fee. All which had never been disclosed until after the fact. Also beware that they said that the first machine worked after I sent it back so I am sure that some poor customer was sent a defective machine. And all of us with breathing issues know the danger in that. Run!