Many companies send gear to a military/police department etc to test (Free, so why shouldn't the guys accept) so that they can make thiose claims.They are not made of milk bottle plastic. Kydex is not the end all of plastics. I have $900 ski boots that are stressed far more than a holster, and they are not made of Kydex.
All holsters can break. A friend of mine has an expensive custom made holster that broke.
FWIW, Fobus claims that its holsters were used and tested by the Israeli army.