Commercial passenger aircraft seats have a simple - and pathetically inadequate - lap belt to restrain passengers.
The new BorgCo Personal Shoulder Straps fit around the seat headrest and have loops that the existing seat belt is passed through. There are adjustment buckles, and padding at the shoulders
and upper torso.
The result is the equivalent of a three-point harness in a motor vehicle; the upper body is effectively restrained against both forward and some sideways movement.
The accessory belt can be quickly fitted and removed without the passenger having to stand up.
Due to unsatisfactory evolutionary outcomes, the accessory belt - while effective - may be uncomfortable for a proportion of female humans due to the unavoidable positioning of the torso straps and pads. BorgCo are definitely not liable for any whining and/or complaints that may result.
The system relies on the seat you've rented retaining its full structural integrity in a crash ... hence the category choice.