FF - first milk and follow-on milk - what is the difference & which do i use?

[choolie]

DS is 6.5mo and BF. Now he's on little meals he wants drinks out of a cup in the day and I want to try him on some formula so that I can stop expressing in the day.

what is the difference between first milk and follow-on milk and which would be best for me to get?
TIA

The iron content is higher in follow on , but not very digestible, and it can be advertised and price promoted so may work out cheaper.

ok, cheers