There are differences in iron, protein, fat content, etc between the Nan Pro and the Nan HA.
We have had DS on Nan HA since he was 5 weeks & have been VERY happy with it. Recently, I mistakenly bought the Nan Pro & found that it was really 'watery' when made up compared to the HA that is really milky & creamy (not the best descriptive words, but hopefully you get me!!).
I think if you compared their nutritional qualities first & then decided!!
When we first started DS on the formula, it took him a couple of weeks to get to do a poo a day (when breastfeeding, he was doing a poo every 10 days, so this was a BIG change!!). If he went 36 hours without doing a poo, I would start on the coloxyl drops (there is also a brown sugar in warm water mixture to help).