Shake diets can be awesome IF done CORRECTLY. Please remember any program like weigh watchers, lite and easy, tiny ferguson etc would not make much money if everyone saw the results they wanted within a few months.......
DH has lost 15kg in just over4 months but he is definitely not following his diet plan 100% - if he did he would have lost ALOT more.
Basically he starts his day with an omelette with 6 eggs - only one has the yolk the rest are only the whites. Add in veggies. No starchy ones like potatoes.
Then the rest of his meals consist of one lean meat portion or tuna in spring water tin. And steamed veggies or salad. No dressing or salt etc.
Meals fill him for 3 hours, then shakes fill him for 2.
You MUST get a shake which has the best nutritional profile. His has hardly any sugar or carbs. Full of protein. And it's a super shred one. He's also been working out, 2hr workouts at the gym 4 days a week.
In regards to plateaus - you should have a 'day off' where you can eat whatever you like (but not large quantities - one Big Mac meal if you please but not 3!) this kick starts your metabolism. First one 4 weeks into your diet and then every fortnight.
DH is now at maintenance stage almost as he only wants to lose about another 1.5 kg. So he is allowed to have one day off each week.
Hope that helps.