嗎 asks whether a statement is true. 好不好 asks whether a suggestion is agreeable, and offers both answers to choose between.
好不好我們去看電影? → 我們去看電影,好不好? (the tag hangs at the end, never up front)
你是學生好不好? → 你是不是學生? (a fact takes A-not-A on its own verb, not the consent tag)
我們走吧好不好? → 我們走,好不好? (drop 吧; pause, then add the tag)
English tags almost any statement (let's go, shall we? / you're tired, aren't you?). 好不好 only tags a suggestion or request, and it always lays out the two answers — never a flat statement of fact.