I used to have a problem with this back when I was uninformed - figured I'd get a used screen, used battery, etc... However, this simply is not the case.
My 6+ red screened on me (kernel panic) within a month or two of ownership. I got a free "refurb" replacement (thanks Applecare+) that I continued to use for 1.7 years. It was a SOLID phone with 103+% battery design capacity (99% after 250 cycles when sold).
After that, I actually prefer refurb devices from Apple. Seriously considering doing what my little brother did last month... He walked in an Apple store, bought a refurbished 6s+ for several HUNDREDS less than a 7+. Maybe I'm getting older but I don't need the latest and greatest anymore.
My wife's 6s+, 1.3 years into ownership, was destroyed by an Apple Store employee took it apart recently. Got a 100% free refurb iPhone 6s+ - 0 battery cycles, flawless screen, flawless back - couldn't tell the difference between a brand new one. I was honestly jealous.
Apple Refurb? Yes please.