Where I play just about everybody take even money for BJ. The wizard of odds say the house has a 7% advantage on this play.
The 7% refers to how much you will lose of every dollar you wager on insurance if you took it every time it was offered.
But even if you take even money EVERY TIME you have a BJ, it'll cost you only between 1 and 2 cents for every $100 you wager while playing due to the frequency of this happening.