i haven't been losing very well on slimming world both doing green (4lbs off in 4 months) and ee (7lbs off in 9 months) with many weeks plateau-ing. I thought it was possibly to do with something with me and after having blood taken a few weeks ago, Dr said everything is fine do 5-2 and only consume 1200 calories a day. The 5-2 doesn't do anything bad to your metabolism, if it does anything it wakes it up, from being on automatic pilot to having to 'work' on food days. I can go without food till tea time no problem, and have my calories in a decent meal and a snack later on if I wish. If I was eating 3 small meals a day, I was finding myself struggling to stick to approximately 500 calories. You'll have to experiment which works better for you.
I am finding it much better limiting the calories on SW as if I plugged in my daily food, I was consuming loads more calories on 'syn free or free' stuff. An example is if you have a mug shot as a snack it is just over 250 calories which should be the bulk of a meal caloriewise if your meals are roughly 350 cals plus snacks. You're actually eating a lot more calories then you actually think you are on this plan. I suggest you plug into myfitnesspal what you've eaten for a day or two and see how many calories you've actually consumed following the plan. Is it worth it to change over? Yes, it's pretty easy too. You will feel a bit hungry until you body gets used to the decreased calories whereas on SW you shouldn't be hungry.
Is it going against SW? Not really you're still following the plan exactly, but you're just limiting the calories a little as they can get out of hand. Some people cope really well on following SW strictly others like myself can't and have to watch calorie intake. Don't forget it's supposed to be a lifestyle change and with that I think it's more to do with people eating more veg, fruit and limiting their junk/take aways intake, basically what we're supposed to be doing anyways.
I have been doing it for about 2 or 3 weeks now and I actually feel/see more of a difference following 5-2 and 1200 then simply following SW alone. I suggest trying it for a week as you have nothing to lose (sorry no pun intended!), and if it isn't for you for whatever reason you can then make an informed decision as to what to do next. How you go about losing weight is your business, and if others start saying you're not following plan correctly so it won't work, don't necessarily have issues on the plan itself. For me, following the plan, but totally taking into account calories from free and syn free choices while still having at least 5 syns has made a difference for me and I can now say yes the plan works for me, but it had to be modified slightly.