It is certainly not a decision making tool or, really, a model to be honest.
The best way I can think of to describe it is as an illustration of how the mental process of decision making actually occurs - a theory. You don't set out to 'do' an OODA loop decision - you just do. Its utililty is in understanding that there are constituent parts of the process, and that by speeding up elements of your process relative to the enemy (ie by orientating quicker due to better observation ie ISTAR) you can make a decision quicker than him, therefore putting him perpetually behind your own process and at a significant disadvantage.
Its like playing 'Racing Demons' - just when you have worked out which card to put down, the situation has changed and you have to start all over. My wife beats me every time.