I'm a fan of biodegradable plastic bags. Carrying my groceries home in such should basicly make biodegradable trashbags obsolete.
But there is a twist. Which might be because both bags are a manufactured in same company. Why cut down the sales of another milking cow, he you can have two. -The reason is that shops might end up Not having plastic bags available, which don't do a proper job either in holding up in one piece till you are home, nor containing your waste in it.
It is somewhat understandable that these bags need to decompose in relatively short period, but does it need to be under a week?! You would expect to have some plastic left when you carry you waste outside..
I made a bit of a field study on this and it seems that 3 months is the shortest period anybody considered the plastic should start decomposing. And most of the people don't work on their own composter..