Maybe not, but when you have an alternative that tastes better, costs less and is better for your overall health, why use the other product? I don't know about everyone else, but I'm doing this to improve my health as well as lose weight and it would seem that eating stuff with hydrogenated fat in it would be counterproductive towards that goal even in small amounts no matter how low the carbs are. After all...margarine doesn't have any carbs, but you wouldn't catch me ever putting that stuff in my mouth! I wouldn't even use it when I was on low fat!
If it's for convenience, I'd go for the Reddi Whip in an aerosol can over the Cool Whip. It's less than 1 gram of carb for 2 tablespoons and at least it doesn't have hydrogenated fat (transfats) in it. I check the "Fat free" Cool Whip at the store yesterday just out of curiosity and even that lists "partially hydrogenated coconut or palm oil" as the second ingredient. How that can be and still be labeled as "fat free" is beyond me, but it's there for anyone who cares to read the label to see.
IMNSHO, nothing beats real whipped cream yet, though. It takes less than 2 minutes to whip and will keep for 2-3 days in the refrigerator once it's whippped.