Been there, done than & failed on the 2nd day
I think liquid diets work if you're very strong willed & to be done in a short period of time.
Low fat diet and exercise is the best.
I've never seen a liquid diet, but I'd say it's probably not safe, because you might not be getting all the nutrients you need. Additionally, fad diets such as that are not meant to be long term, so any weight loss would most likely be regained once you go off the diet.
Healthy eating and moderate exercise are the best way to lose weight.