3ab77246_Murphy_Beds__Other_Murphy_bed_mechanisms
Piston lift mechanism is COUNTER-BALANCED and designed for daily use. Piston functions so "it doesn't know it's working" and is not subject to metal fatigue or catastrophic failure [Other Murphy bed mechanisms] 
Springs expand and contract and fatigue with age, causing bed to sag out of cabinet. Springs are expensive and difficult to replace. If spring breaks, catastrophic failure results
Murphy Beds
Other Murphy bed mechanisms