in the past i have been down a similar road and i will honestly say after finishing i ended up putting on more weight than what i had just lost and it doesn't train you to eat for your new body when you've finished.
a body that weighs 140lbs needs less calories to survive then a body that weighes 200lbs.
just as long as you go into it knowing you will have to adjust your diet majorly when you have finished not only becuase your body will go into shock from going from a shakes programme to eating normal food again but also adjusting it for your new weight and body then i say go ahead. just don't go into it thinking you can revert back to your old ways once you have finished. i did that and it was a big mistake!
I'm now doing the old and simple way of eat less move more, with the help of loggin everything on an weightloss aid app (my fitness pal) strangely enough this is the first time ever i have managed to keep motivated and carry on doing it. most 'diets' 'fads' or whatever last about 2 weeks for me then i get bored, loose motivation or whatever you want to call it and give up then more weight piles on. i have been doing this 4 weeks now and am loving it, i have lost 6lbs now and my brand spanking new pair of jeans i brought myself in the first week of july (size 16UK) are now falling down round my ankles when i walk lol.
its helped me track my exercise (cardio and toning/strength) and it helps me to adjust my calorie intake for the ammount of exercise i do (the more exercise you do the more calories you need for the day so your NET total = your set daily goal mine is 1380 calories a day, i burn 500 calories in a day exercising i need to eat an extra 500 calories otherwise my body is under nourished for the day as it would be like i have only eaten 880 calories)
sorru to go off on one i was just trying to get my point across that perhaps your not eating enough to make up for the calories you loose whilst exercising and perhaps a tracking app like my fitness pal (or one commonly used in Aus) might help you see you back on the right path.
always here if you want to chat, im loving the new me! never thought i would actually say it but for once in my life i am enjoying exercise and loving the new healthier changes to my body, i am a convert lol.