Bullets are cheaper and ropes can be reused.
I can understand companies not wanting their drugs to be used for executions. Just use heroin.
They absolutely proven to be painless.
They are 100% effective. Life cannot continue in the absence of oxygen.
An inert gas such as helium or argon replaces the atmosphere in a sealed room. As the oxygen is displaced the condemned loses consciousness and dies.
Because an overabundance of carbon dioxide is the cause of the pain of asphyxiation and not the absence of oxygen the removal of the CO2 in the room also removes the possibility of pain during this form of execution.
The anti-death penalty crowd could not reasonably oppose the use of inert gases on the grounds of pain induced by the method of execution.