Nipple flow - Bottle


My son is mostly breastfed but has atleast 1 bottle of pumped milk a day. Currently I’m using 0-3 months slow flow nipples. With my formula fed baby, we moved to the medium flow at 3 months. Do you change nipple flow with breastfed baby or continue to use the slow flow so they still have to work a bit for it? Or will baby get frustrated with the slow flow?