Follow on milks are basically developed to get around the advertising rules relating to first milks. Thye companies can't advertise milk for babies under 6 months and can't offer incentives like points on shop loyalty cards etc. They do contain more iron which some people find can cause constipation - we moved DS to the cow & gate comfort 2 but soon moved him back again for that reason.
Babies lay down their stores of iron in the last few weeks in the womb, so a healthy full term infant should be fine on normal stage 1 milk until they are 1 year when they can swap to cows milk. The stored iron does start to decline but I think more recent research has shown it isn't such a big need to supplement as previously thought.
You are fine to carry on with the stage 1 milk!
Laura
