To be honest, my son is still using the newborn or anti colic one for tomee tipee bottles… because he finishes the bottle in a good time, and he gets choked up on my let downs sometimes, so don’t want to do that when he’s bottle feeding
If you don’t see your baby struggling or getting lip blisters from the friction it might be ok flow for him. If you do think you need to increase flow I would do so gradually because the change would be too drastic if you skip levels quickly and if your baby doesn’t understand the fast flow it could cause him to choke and not want it anymore. Babies usually are visibly frustrated when they aren’t getting their milk fast enough out of the bottle so just watch for those signs.
My now toddler nearly 2 stayed on number 2 MAM nipple until he got off the bottle. Some babies dont like a fast flow