The figure 8s from Ace Metal Products likely use a cheaper alloy... compared to some other manufacturers that might use 7075 aluminum, which is harder and will last longer. I'm sure there are differences in the manufacturing process as well.
... and, yes, ratings and specs are often not comparable between manufacturers (because some are conservative and some more liberal it seems with their numbers).
I don't have a problem with AMP (I have purchased from them before), but we all need to do our best to disclose where something is made, how it is made and what it is made from. Easier said than done, unfortunately.