No extra fees, just the .16/mile + sales tax. To me, unless you're 100% sure you'll use 12k, there's no reason to pay for it up front. With other brands, it may make sense to buy up front.But with the way BMW let's you do it for only .16 and they give you to damn near the end of your lease to do it? No brainer... You can always add miles, but you can never get a refund for what you don't use (at least not yet
. I think some brands do offer that now).