Well, I've never tried Slim & Save, but having just looked at their website, it does appear to be the same sort of deal as LT. 3 sachets per day of 450cals etc. One slight thing that makes me wonder, though, is that it says "A mild ketosis may develop" - which doesn't seem as strong as LT's aim of definitely getting you into ketosis and keeping you there...
Why is it that you're asking? Is it the extra flavours that you want? Again, as I understand LT's aim, having dull and boring flavours is part of the plan! Both to physically cleanse your tastebuds and to psychologically break any taste addictions that you may have to junk-type foods. The reasoning is that when you DO start eating again, your body and mind don't automatically want to go straight back to strongly flavoured fatty, salty and sugary foods, but will instead be able to appreciate more subtle flavours of the healthier things...
If it's just an occassional item here and there (in a similar way to how Dee described the Atkins bars) then I don't think it should be a problem, but you'd have to monitor it carefully for yourself, I guess. As she said, it could be the start of a slippery slope towards craving "proper" food too early!
Maybe you might want to switch completey over to S&S, but then you'll miss out on weigh-ins, so it depends how important they are to keeping you on track.
From your stats so far I think you're doing brilliantly - your average losses appear to be about double what mine are!
I'd be rather inclined to say "if it ain't broke, don't fix it", but of course only you know how you may be struggling...
Best of luck, whatever you decide,
Marianne x