Yes, it is absolutely fine to enjoy NICK'S if you adhere to a Weight Watchers diet or any other low-calorie diet. If you want to know how many SmartPoints each product has, this is available in the Weight Watchers application.
SmartPoints are based on a combination of calories, fat, carbohydrates and sugar. You can always count on us to always have a lower calorie content than the biggest competing market leader (eg Biscuit Bar vs. Biscuit Chocolate, Coconut vs. Bounty and Peanuts n' Fudge vs. Snickers).