Scootrd,
I have not used one of the two you provided links for, however, I can see good possibilities for such a product.
I have used a product, which would not probably fill your completely hands free needs, and find it works very well.
Back a number of years I started having problems carring a rifle by hand. My arms would ache and go to sleep, in short it just wasn't working.
Living here in Ideeeeeeeeeho, where the cover many times requires quick response I tried to down size weight wise and found that less then a good answer.
What I did find, was the Boonie sling which allows for an across chest carry of the firearm, with the weight supported by a wide strap over the shoulder.
Calela's sells them, but not sure that the Boonie name is correct any more.
The rifle is instantly ready to be brought into firing position, while taking the strain off the arms and shoulders.
Because of this sling, rifle weight is no longer a problem.
When I hunted in an area that was best hunted with a pack frame carried in with you, my rifle always needed to be carried by hand. Given my present shoulder/arm situation, something like you list would be my only way to continue hunting that type of country.
Personally, provided the rifle is secure, the chest carry style looks the best.
Keep em coming!
CDOC