Clark, the Atlas NS is very easily flexed, like if you hold a piece of it out horizantally, with the ties perpindicular to the ground, it droops.
The steel flex track I had (Model Power) was attracted to a magnet, and the ties make perminant indentations in your skin when you attempt to flex it. It offered similar pleasure to that which is derived from running a cheese grator across your knee cap. Also when it corrodes, it had a very white-grey ashy apperance and the corrosion was non conductive. Corrodes fast and difficult to solder. That property might be specific to MP, but I expect the stiffness and magnetic properties are universal to all steel flextrack. Needless to say, I only bought MP flex track once, and it's now in the landfill
Stainless Steel may be a whole nutter matter.