If you are going to be doing a purely cardio program then you shouldn't be using a PH. PHs have side effects including back pumps and lethargy, which can make cardio very hard or pretty much impossible to do. This will be even more evident with a cardio program like Insanity where you are doing a lot of jumping and squatting movements.
If the diet is working well for you then stick to it. Adding in Insanity to a diet that is working will mean that you should speed up the fat loss. You could add in a couple of weight training days to help you retain muscle and assist in leaning out if you like but there isn't any need for a PH.