I hope you see the result of good practice just i think

This phrase is mostly used when someone is selling something and by saying it he/she wishes that the sold item be beneficial for you and you use it happily.

kheili mamnoon, saeede joon

it is as you said: may it brings you luck/ may you benefit from it. but "kheir didan" has another similar meaning. "kheir bebini" is used as a thank you to someone and it means "may you be happy and successful" and "kheir nabini" is used as a kind of curse.