It works but like any diet, it only works if you change your eating habits and change them for good. Like any diet, if you stop following it, you will put the weight back on.
I lost 2 stone a few years ago, but put it all back on by not continuing to eat properly.
But prior to SW I was not eating breakfast, not eating proper meals, lunch would be sandwich/crisps/kitkat type of thing, tea might be cheese & biscuits or a bowl of cereal.
Once I started SW I had breakfast every day, lunch of overnight oats/porridge pot/potatoes and ham/cheese, but most importantly I cooked a proper meal every night of chicken/ham, potatoes, carrots. (I don't like veg/salad so very limited in what I can eat to diet).
I started out using the syns for sweets/crisps etc, then over time realised that it was better to use them for gravy to improve a meal etc. It did change my thinking.
But I didn't need to be a SW member to cut out the crap and eat proper meals. What it did was focus my mind on what I should be doing and what I should cut out. SW also encouraged regular exercise as well .
I would recommend it, but you do need to see it as a long term thing, as any diet should be, you need to maintain once you have lost the weight.