Other than a pawn shop FFL is trying to get you to buy a BU, why do you feel the need?
Not that "I want one" is not sufficient, at least in my book. But do you just want one (I'm thinking "No" because of finances) or is there something in your life that makes you feel that you "need" one?
Now, if you are thinking about having a "spare" in case your primary carry goes Tango Uniform and has to spend time at the gunsmith for repairs, then a back-up makes sense as a plainly practical matter, as in "One is none and two is one".
From a personal perspective, if what I'm carrying in the gun + any reloads (extra magazine(s) or speedloader(s)) is not enough then I needed reinforcements a while ago and should have slowed down the expenditure of my ammo. (Aint hindsight just wonderful?) But that's just me. YMMV.