I was also going through the same thought. Checked with doc and few friends, they are saying no to formula as it impacts the immunity of child. My friend who has 2 kids says she saw the difference exclusive BM made to her 2nd kid's immunity as compared to the 1st one. ! So decided to feed her BM through bottle as she might not accept it later . My pediatrician told me that we can keep BM at room temperature for 6-8 hrs. Hope it helps.

i m thinking to feed breast milk as well as formula through feeder..

No..either breast or bottle..what do you want to feed in a feeder?