The differences between the two are the price, the gel serum foundation is £1 more than the original healthy mix. The gel formula is supposed to blend a lot easier than the original but other then that I couldn't find any other differences.
I have to admit I really do love this foundation (watch out for it in my August favorites as it is currently residing in my favourites tub at the moment). It applies so smoothly to the skin and creates such a great flawless look and doesn't look cakey on the skin.
The foundation last quite well on the skin, I wouldn't say 16hours but I would say that it last a good 9hours (during the walk to work and while I am at work).
I loved the original and I love this one but out of the two I think I would pay that £1 extra and go for this one as it just seems to blend really well on my skin
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