I've tried it a few times on seperate occassions, and I managed to lose about 10lbs, maybe more? each time. That was until I read 'and a <600 kcal meal and snacks between meals' and thought 'ooh so I can have 2 milkshakes and 900 calories a day, wow! I'll not snack and have a chocolate cake tonight then'...don't do that, it defeats the point of it :P
It is good, I think, though I know lots of people will no doubt say its stupid, unhealthy, etc. I think though its lacking in fibre a bit so you might feel the consequences of that...its also quite hard to get your 5 a day when you're not actually eating 2/3 of a days main meals, so you could get around that and the fibre issue by making sure your snacks are fruit or veg, and your 3rd meal contains lots.
My favourite milkshake was the chocolate one, but the meal bars are disgusting, I thought. Reeeaaally manky tasting.
I generally found it easy to follow, kept it up for a month, I think, each time, but as I said, when I saw the calorie restriction more like a goal, thats when the weight loss plateaued and I just gave up, and then of course the weight came back on (maybe a reflection on slimfast but this always happens with me anyway)
You might not see an awful lot of weight loss in just a week, probably just water weight, but I think its probably a good idea using it to kick start a diet.
Good luck, anyway
Feel free to ask me any more questions x