Good - it will do what it's supposed to, and as such it's excellent to add to every meal to make sure no traces of carbs/fats get through when you are supposed to have protein only meals.
Bad - you can psychologically rely on it. You might cheat the diet thinking that you can take the pills and you won't have to worry about the bad meal. While to an extent that is true, and they would help you out when you cheat every now and then, if you start cheating frequently, relying on the pills, your diet will be screwed as obviously you are not having the proper macronutrients in the quantities and times that you are required to.
So, it's good if you use it for it's purpuse and you don't rely on it to 'diet' for you.