I have been involved in the airbag/seatbelt industry for over 25 years. Although I cannot offer any help on AmSafe customer service, I can give you a little insight into the engineering/restraint logic behind an inflatable seatbelt.
The general lap shoulder 2" automotive type seatbelt exerts a fairly concentrated load on the body during a crash. If worn correctly with the lap belt low on the pelvis and shoulder strap over the shoulder they work pretty well. If the lap belt is high over the soft belly and/or the shoulder belt is to far into the neck or off the shoulder the belt can cause substantial injury itself.
Submarining, or sliding forward under the lap belt due to loose or misplaced belt routing can be very injurious. That is where a crotch strap comes in, holding the lap belt low and preventing submarining.
Back to the shoulder belt. By adding a second strap (dual shoulder straps) you split the localized belt loads on the upper body by spreading the load over two locations. You also maintain a better routing over the shoulder in most cases giving over all better load transfer. This is where the inflatable belt comes in. The belt expands the footprint of the belt spreading the load over a greater area of the upper torso (much the same as a dual shoulder belt) and lap if the lower section also inflates. That is at the expense of a bulkier belt (a small long airbag tucked into a cover that doubles as the standard belt) and the pyrotechnics, sensors and wiring required to sense the crash and deploy the belt.
It is a good solution if greater restraint is needed than a standard lap/shoulder or racing harness can provide.
Two things to understand.
Occupant restraint assumes the occupant compartment and belt attach points remain intact i.e. maintains the restraint force and nothing comes into your space. No restraint system can help if the occupant space collapses or the belts come loose.
Also the belt loads need to be transferred to an attachment location that can bear the loads. Typical in an automobile 25 mph barrier crash is 2000-2500 pounds of force. For example attachment to the seat back is useless unless the seat back can withstand that load. Otherwise the seat back just moves forward with the occupant on his/her way to the instrument panel.
Good luck with your choice.