Let me address a few comments here...
1) For those concerned about passenger contact...
Please read the warning label
If you are planning to have passengers to the rear of the mount...Just don't buy it.
From the website:
Any product can be misused and thus present a danger to its user. Please read our guidelines to using this product safely.
This product is designed for military usage and for off road competition. Please use the product responsibly.
Please do not hang items on the mounts that will limit rearward vision.
The MPAC Back Pack hook is designed for light cargo only, please check with your vehicle manufacturer to determine the weight limits that can be applied to your seat safely.
This product is not meant to restrain cargo. It is Springtails opinion that all heavy/dangerous cargo should be confined to the vehicles cargo area. Furthermore all cargo should be restrained in an adequate fashion to prevent any potential movement into the passenger compartment.
At no time should this product be used with a passenger positioned to the rear of the back pack hook. In the event of an accident or unexpected maneuver, a passenger could be seriously injured or killed. The product should be removed if there is any need to place a passenger behind the mounting area. In addition, care should be taken when accessing the area to the rear of the mount.
Springtail supports the use of safety belts and the practice of safe driving techniques.
Too much weight on an unoccupied seat may set off chimes and activate airbag sensors. Take care not to use straps that may impede with side airbags or restraint systems. Please use the product in a responsible fashion.
By installing this Springtail product you are acknowledging that there are potential risks from misuse. If you do not accept these conditions, please return unused product to Springtail for a prompt refund.
In addition: If you place the mount in your mouth, it can also serve as a choking hazard
2) Making the Mounts in Plastic...
a) Besides being extremely inferior to steel in this application...the cost of plastic molds are astronomical. It makes sense to make plastic molds when you are planning on selling thousands of copies. Since Springtails focus is on very specific niches...we can make quality products for very specific purposes. That is why our products fit and function very well.
btw: Plastic will mess up your face just as easily as metal....quick reference back to the warning label.
3) "The way I drive, the bag would be on the floor in no time"
I am not exactly sure how you drive

...the hook concept was developed with the intent of living up to the rigors of the military and off road competition. The whole concept was devised at the request of some Military operators in the middle east.
If you can shake something off of the hook with your driving...you may consider using the carabiner option with the mount or a bungie under the seat

I have spent a few months with prototypes in both my FJC and my GMC Sierra. Both vehicles are used around the farm and see pretty rough territory...nothing has hit the floor yet.
4) Cost
The cost is based on the expense of making the unit (this includes laser cutting, forming, powder coating etc). So far all of the back pack hooks have had about the same production cost.
We use local resources to manufacture our metal goods so while the cost is a bit more...we can assure that the quality control is outstanding and the supply is appropriate for the demand.
We are not out to scalp anybody...but in the same respect, we are not in business to lose money either.
I would anticipate a similar combo deal for the FJ80 crowd as we did for the FJ Cruisers. Give or take: $20 each or 4 units for the price of 3 (~ $60.00)
Doc