I'm not the person you asked but I've done slimming world on-and-off for about 15 years. It has a lot of pros and cons. I'd recommend the podcast The Secret World Of Slimming Clubs to find out more
Pros
- If you have several stone to lose you probably will lose quite a lot quickly by cutting down on 'junk' food. Women below 16st are allowed 15 syns and all men and women above 16st are allowed 25 syns. If there is no 'healthy' food component then one syn is equal to 20 calories so most people who go have up to 300 calories in syns.
- If you follow the rule that 1/3 of your plate has to be speed food (aka non-starchy fruit/veg) then that's going to cut down your calories a lot by default and help you to lose weight as well as getting you lots of good vitamins and nutrients.
- You are recommended to have two dairy (or vegan) sources of calcium and one source of fibre (such as brown bread or cereal bars) per day
- It can be good if you don't do much cooking as it encourages home cooked meals (though they do sell their own ready meals)
- Having a place to go to every week for support from people who know what it's like to be overweight is nice, especially if you don't have the support in your private life
- You can get useful tips and tricks in group
-The members pack explains that you need to be in a calorie deficit to lose weight and that the plan works by reducing your calories by replacing 1/3 of your food with speed
- Some of the recipes in the cook books are nice
Cons
- You can get a very mixed experience with consultants. Some are good, some are dreadful. It can be the same with groups as well - some are just super cliquey.
- The term Syn is bad. They say that it stands for 'synergy' but if you look at booklets from the 90s they were called Sins so it does mean sinful food. Even with trying to rebrand it can still have an effect on members and it isn't unusual to hear someone sit and talk about eating 'naughty food.' If you go above your syns you might feel so bad that you binge (I have in the past), even though you could have been under your TDEE before the binge.
- If you suffer from binge eating or just have a very large appetite it is possible to stay within your syns and have 1/3 speed but still eat above your TDEE.
- Many leaders will never mention calories. A lot won't even mention portion size. I've sat in groups with people crying because they haven't lost anything in several months with the leader saying "oh, well increase your speed a bit more and maybe you'll lose next week."
- If you don't have much weight to lose you'll find it a lot more difficult
- Some people interpret 'unlimited free food and 1/3 speed' to mean 'an entire plate of pasta with one shallot' or they increase their portions by 1/3 to add the extra speed on rather than reducing and replacing with 1/3.
- You can easily fluctuate in weight for reasons other than eating. Most leaders nowadays will just say "oh, you've had a bit of a gain this week" but a few will still say "oh, you've gained two pounds this week" in front of everyone.
- Even though SW technically promote 'body magic' (aka exercise) in all the groups I've been to people avoided it like the plague because they didn't want to get a gain on the scales
- There is a big push towards buying the bars and other products. A lot of SW consultants get almost no money from their classes though so I don't begrudge them that.
- It isn't uncommon to find people drastically restricting on weigh-day (such as weighing at 19:30 so not eating after 10:00 and not drinking after 12:00) and then eating five SW bars as soon as they're weighed and then going home and having loads of food because they're trapped in a binge-restrict cycle
- The meetings can get annoying. When you hear "I don't know why I've gained weight four weeks in a row, I've followed the plan perfectly" it is hard to not shout "you're eating too much".
- A lot of the syn rules don't make much sense - if you eat a banana it is free but if you mash it up it is syns - if you have dried pasta it is free and unlimited but if you have fresh pasta it is incredibly high in syns
- A lot of people will end up scared of higher fat foods like olive oil and avocados because they are higher syn than chocolate bars
- A lot of people will eat the max amount of syns per day, even if they're not hungry, because you can't roll them over
- When you get to target you are allowed to go within -3 or +3 pounds and if you weight anything else you have to start paying again, even though you may be a perfectly healthy weight.
edit - Thought of another couple
- It is possible to go too low calorie. If you're having a small amount of cereal and skimmed milk for breakfast, a vegetable soup for lunch and a vegetable stir fry (in fry light) that is not going to be anywhere near enough calories long term and you'll end up breaking and thinking it is because you can't stick to a diet when the diet was unhealthy
- You get people making horrible desserts out of quark or sausage rolls out of wraps and saying "syn free" when they are often more calories (and taste much worse) than having an actual cake or small sausage roll.