I’m not sure any of those are full diet replacements though. They serve as a good breakfast or lunch, but I don’t think it’s recommended you replace all meals with them. At least not in more ideal circumstances.
So yeah, with a 1500 calorie deficit diet, that’s about a 3rd of what you eat for the day, so like 33%. That’s a pretty big chunk, and easily allows you to snack on occasion and still hit your deficit. I’d say it’s pretty helpful, but diet is still absolutely necessary for any results.
I’d say it’s more like 70/30 personally. It also gives you some wiggle room with a low cal diet. But you definitely can’t just do some running then go out for bucket of KFC all the time.