unless you are a cop a BUG is overkill and potentially a bad idea. your chances of needing your primary are low enough that the odds of needing a back up are incredibly slim. on top of that consider if you do get into a life threatening altercation. you may get prosecuted and you will be portrayed as a gun nut itching to kill. in the eyes of an ignorant jury the fact that you had two guns would pretty much seal your fate.
oh wait you carry a glock, yeah a BUG is probably a good idea