I've lost weight on it and definitely prefer it to weight watchers which never worked for me. I was much less hungry on Slimming World.
It's fairly easy to follow and is healthy in that things like fruit & veg are unlimited. I guess the negatives are all that bloody quark. 🤮 And I hated the meetings - am introverted & definitely not a joiner!
Getting weighed was a good incentive to follow the plan during the week.
There are some good 'unofficial' recipe books that use the SW principles like Two Chubby Cubs and A Pinch of Nom. Though these would work while following any healthy eating plan.
The only thing I'd say is that once you do lose weight it's a doddle putting it back on. At some point you need to stop and maintain it and, if you're following any kind of commercial plan with sometimes mysterious principles (syns, points etc), that can be challenging. And I think sometimes fatigue sets in after a honeymoon period. Don't want to be a misery but I put it all back on and a bit extra! Though COVID didn't help.
I think it works best for those who love the meetings and enjoy maintaining their weight while still on the plan & are happy to do it forever! And of course meetings and weigh ins are not possible at the moment which takes away the group, social aspect.
So something like Noom or My Fitness Pal, where you count calories and learn more about nutrition / health for the long term may work better for some. 