Dear user, u need to be precise in your query. As meal replacement product is very broad segment.
On a very broad background, to tell you , these are the products which are recommended by nutritionists / doctors, for individuals who are overweight or obese.
The basic principle behind this is , to cut down the daily calorie intake of that individual. As sometimes people can't manage to cut down their calorie intake with their regular diet patterns.
Next Steps
I think you should talk to your doctor before planning to have those.
Health Tips
But , in my opinion, if someone reduce calorie intake in their regular diet pattern, it can be sustained on long run.
As for any new product per se, no one continue it for long term.
And if someone goes back to thier regular meal plans after stopping LOW CALORIE routine, they tend get overweight again.
All the best...