I think they work fine if you add actual ingredients or meals from a huge fast food chain (that comes with a calorie chart) or prepackaged food. But with whole meals it simply doesn't work. There is just too much difference in the portion sizes and the fat content. So for people who eat at restaurants a lot or order take aways it's pretty much useless... Obviously, a lot of eating out and take aways is in general bad when it comes to weight loss - the people preparing it don't give a  fuck about your health, they just add whatever makes it taste good and that's usually fat.