You'll probably get one use of that, then. I doubt they'll still have 2012 Macbook Pro batteries sitting around in 2018, much less a person who knows how to install them.
I took my 2006 Macbook in to an Apple retail store to get a new battery, and they don't stock them any more. They said they could special order one, but actually suggested I try Amazon.
And I hardly think saving an hour at an Apple Store once every 3 years is worth having a substantially thicker device.