is it really good this feed and weed chemical for lawn ? Would it disturb my peonies and other flowering?

The label on the fertilizer bag should tell you what the weed killer will and will not harm. Probably most flowers, being broad-leafed, will be harmed.

Although I've used weed 'n feed fertilizer on my lawn, I really prefer to spray weed killer on the lawn using my garden hose. It comes in a small bottle with concentrate inside, you screw it onto your hose, and walk around spraying the yard lightly. One bottle covers typically about 5000 sq. ft. and costs about $ 10. It takes about 10 minutes to spray one bottle.

i would not use a weed "preventor" this will stop your peonies from regerminating. just make sure your weed and feed does not say"weed prevention or pre-emergence on the lable".