Ester-C is a non-acidic form of Vitamin C. I have been taking it for quite a number of years. Some sources claim that Ester-C contains metabolites that may enhance the delivery of essential Vitamin C to the cells of the body, resulting in higher blood levels. On the other hand, there are some who dispute this claim. My guess is that it's at least as good as any other form of Vitamin C, and since it is non-acidic, high doses will be much better tolerated. Of course, it is also about twice as expensive as ordinary Vitamin C.
Ester-C is is not a different "form" of vitamin C in the true sense. Actually it is still ascorbic acid only it is bound to calcium. This can do two things. One, the caclium reduces the acidity and two the ascorbic acid releases slower, breaks down slower allowing for a somewhat enhanced opportunity to absorb the C. Absorption time of ascorbic acid is rather short, generally 2 hours or so, being bound to calcium gives it approximatley 3-4 hours. Higher intake of esterfied c will alleviate the sometimes bothersome acid tummy with some people. M