Ketone sticks

I have read several places on this site that ketone sticks are worthless. Is that because they understate how often one is in ketosis, overstate it, or are just generally unreliable?

Ketones do not necessarily show up in the urine even when in ketosis if used for energy production. So if for example, one was performing quite a bit of cardio work, which often goes hand-in-hand with a ketogenic diet, then the urinalysis may suggest that there are minimal ketones in the urine.