The main reason pro haunts use professionally made cylinders is very simple. Liability. If something happens with a pro cylinder and somebody gets hurt, the blame can go to the manufacturer of the cylinder. If the cylinder is homemade, the haunt is totally liable for the injury and can even pay more in damages for using "unsafe" equipment. A good way to lose all your money and the haunt.However you do raise an interesting question. If people who make homemade cylinders consider them reliable, why not use them in pro haunts too considering the cylinder is never seen?