I can tell you from first hand experience that a certain commercial extension tube that comes from a manufacturer that starts with a 'B' did fail when the rifle was dropped off of a shooting bench and fell stock first onto a concrete pad.
Distance was 48" of drop, rifle impacted on left side edge of collapser stock and the force broke the stock latch and bent the extension tube at the junction of the castle nut severe enough to render the rifle unable to function.
Wasn't even a "combat malfunction", the rifle fell off a bench, something that happens pretty frequently, probably much more frequently than combat damage occurs to civilian owned AR15 rifles.
I now use VLTOR mil-spec+
extension tubes, (the genuine ones, not the made by someone else in Illinois versions.)