Keto urines strips are a great and cheap way to test your ketisis levels hen heading into a keto diet.
However their one drawback for long term use is that, because the volume of ketones are tested in urine, as the body adapts to producing and burning ketones it can burn more of them as fuel, meaning that less pass through in the urine and potentially giving an inaccurate reading.
That is one reason why ketone blood testing is far more accurate as a long term option, and also breath testing.