I did 4 shakes a day for a while and my losses were exactly the same as on SS normally 4-5 lb a week on average , the official average is also the same as SS at 3.5 lb a week
I always had 4 shakes (5ft 71/2"). My CDC advised it as I was a regular gym user.
I don't think I would have stuck with it without having the 4th shake as a hot chocolate at 9pm as I was always starving by then. Still lost a stone a month!