Straight pipes are inefficient because they require a lot more compressed air than a properly designed safety air pistol does to provide the same amount of thrust.
Straight pipes are frequently controlled by a ball valve, which lacks the "dead-man" functionality found in the safety air gun trigger mechanism.
Straight pipes are not ergonomically designed tools, hence they cause operator fatigue over time.
As the straight pipes do not adhere to the OSHA guideline limiting output pressure, which is less than 30 psi when dead-ended, they are unlawful and dangerous.