When I cut bfing out completely at 14 mths and moved to food entirely I did use follow on milk as for a little bit I just liked the thought of it having extra vitamins. I used it in 2 bottles only morning and night. I gradually phased it out switching fully to cows milk by 18 mths once I was fully confident in dd diet.
I found it a nice crutch for a little bit. Thats all it was in my personal experience. i think cows is probabky sufficient and certainly less sugar....! I do also keep a carton or 2 in the car as emergency ( incase of traffic etc as dd likes milk/comfort alot). I switched fully because of foreign holiday and for two weeks no access to formula. Seemed idiotic to return then....
I see no value or benefit in follow on milk, if the child has a reasonably balanced diet.
The only purpose for follow-on milk that I can can see is that it is allowed to be advertised, and thus creates a presence for the infant/first milks that are not allowed to be advertised (mangled grammar but I do hope you get my point)