i have tons of Threadart cotton solids and variegated. every huge once in a while, i see teeeeeeeeeeeeeny tiny knots in the solid thread where the lenghts have apparently been tied together to roll a full spool. at high speed, the thread breaks as those knots hit the eye of the needle.
i have had absolutely no problems with the variegated cottons.
i don't know yet about their polyester. i just ordered some for the first time and it hasn't arrived yet.
for the price, it's great. when i'm in a position to afford to pay a bit more, i think i'll shop around and try a different brand for my solid cottons.