خیرش را ببینید Translation
the literal translation is: May you see its benefit (returned to you)? (real meaning: may it bring you luck)

خیر: welfare, benefit ?

Question

خیرش را  ببینید Translation
the literal translation is: May you see its benefit (returned to you)? (real meaning: may it bring you luck)

خیر: welfare, benefit ?

Answer

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

Answer

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.

Answer

kheili mamnoon, saeede joon

Answer

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.