It's not a con/cult but it depends on which way you 'do' it. I looked into it when pregnant to lose baby weight. I loosely followed parts of it. Stripped back, the main principles are lots of fruit, vegetables, salad, meat, fish, eggs, etc with the odd 'treat' thrown in. Follow it sensibly and it's great.
Eat the processed crap or take the 'free' foods too literally, that's when it becomes a load of nonsense. I've seen on some Instagram accounts, someone had 80g of oats, plus PILES of fruit for breakfast then a massive mound of pasta for lunch, curry with tons of rice and chips for dinner. Or two jacket potatoes with an entire tin of beans then one piece of limp lettuce for 'speed'. It's the latter lot who will have trouble losing or gain it all back.
I've lost 3 stone following nsome of the basics (having lots of salad alongside my sandwich or vegetables with dinner, measured cereal, etc). I didn't do the whole syn shit and still have full fat, olive oil, etc. But it depends entirely on how you follow it.
Cool with lots of fresh food etc and watch portion sizes and it can work. Live off Miller lights, hi fi bars, mugshots and its full of processed rubbish.