So if you are looking at a biodegradable product, you should check whether it complies with the above standards. It is better to look for "compostable" as that implies compliance with those standards (at least if sold in the US or EU).
The standards have been criticized because they assume an industrial or municipal composting environment (which mostly differs from normal environments due to relatively high temperatures). So even if you have a compostable plastic it is better to put it in a compost bin and have your municipality compost it in an industrial manner.
But the compostable plastic under those standards will degrade under normal environments too it will just take longer. Even in your article, the compostable bag disappeared in the underwater test and disintegrated in the open air test. It only survived the under ground test, probably because of lack of oxygen.
So in summary compostable plastics should be composted and not just tossed away anywhere. But even if they are tossed away at random places they will degrade much sooner than actual plastics and thus present much less of a problem for the environment.
