Inputshaft,
First, recognize (unlike zalt) that we on the supply side of this collective effort provide what our customers want and need, so any discussion of the relative merit of SS6 floats is nearly academic - we deliver what you folks want to buy.
The issue is not that any particular piece of kit makes things "safer", because by that logic, we pile it all on until we are absolutely as safe as can be, and carry one passenger in a 50,000 lb machine.
The question is always "What is the next most valuable pound of weight and dollar of cost going to buy that makes the aircraft safer?" Example: should we spend 100 lbs (invented number) going from SS5 to SS6 on the floats, or provide 100 more horsepower when OEI? Both weigh 100 lbs, which makes the aircraft safer? Which do we burden the aircraft with?
That is the essence of design, and operators, manufacturers and regulators all dance together to balance the equation.