You can definitely lose weight on it because I have several friends who have but you've got to apply a bit of common sense otherwise it's like people become utterly brainwashed by it!
I have had quite a few 'heated discussions' with a friend of mine because she falls into the 'brainwashed' camp.
In fairness, she's lost about three stone but bloody hell, she won't have it that SW doesn't promote a healthy eating attitude. She seems to think that cooking chicken in diet Fanta or Cola is far healthier than a fruit smoothy or an avocado salad!
Similarly, she raves about her rice pudding thing she makes and stressed how it's zero syns and she can eat as much as she likes!
I've tried saying that's not a healthy relationship to have with food but she's too far down the brainwashed road.
If there are biscuits or cakes in the staff room, she'll wring her hands and stress about how she shouldn't and will proceed to eat a bloody crumb or two! Utterly ridiculous.
At the end of the day, SW is a business. They have connections with various food manufacturers etc and promote these endlessly. They also rely on repeat business.
Healthy, sensible eating and some exercise is the way to go.