Are these neck massagers safe to use?

r/massage and r/MedSpouse threads in the signals flag two recurring cautions: don't use shiatsu massagers or massage guns on the front or sides of the neck (only the back muscles), and limit sessions to 15 minutes to avoid bruising tissue. Reports of serious injury are rare but documented. People with cervical spine issues, recent neck injury, or vascular conditions should consult a doctor first.