I cannot give you an answer and need to read more on it, however, I am skeptical... it may be better... I do not know.
That said, am I correct in understanding that most of this "nano calcium" are nano particles of calcium carbonate?
"nano" bothers me some... I have read too many negative articles on "nano".
Some of what I gathered, one from a National Geographic article on the subject stated that nanometer-sized particles of TiO2 and ZO (minerals contained in many sunscreens) may be unpredictable in regards to safety.
I would approach with caution at this point. Mike Adam's at NewTarget states that "nano" is the next big "headline" and "marketing gimmick" in the supplement industry and to use caution as well. Mercola, at his site, has written more than a few negative articles on the use of nano technology in sunscreens.