Pat,
The reason you can't leave thawed breastmilk at room T is that many of it's
immune components are dead- living white blood cells are no longer living
after being frozen.  The milk that keeps at room T is just pumped, even
refridgeration begins to kill wbc's after about 48 hours.  Clear?
        I would be cautious about A---t.  They sell 2 nipple sheilds in every
"breastfeeding" kit.  Was unimpressed, to put it charitably, with their
breastpump (tested it with multiple subjects).  This implies either ignorance
of the physiology of normal lactation or a lack of ethics: marketing products
purely for profit's sake without regard for the potential harm.
My humble opinion.
Catherine Watson Genna, IBCLC