In a first, an American woman used a suicide pod to take her own life. The process took place in Switzerland. It’s done by pumping in only nitrogen gas, so the person will lose goes dizzy, loses consciousness and eventually dies. Enter futurama memes.
I would think a chamber is easier to accommodate different body sizes and forms, thereby making fitting unnecessary. Also I would assume it is easier/ less stressful on the operator, since they just lay down instead of having something strapped to their face.