Apple’s refurbished computers and devices are one of those best kept secrets. You still get a full warranty (I think you may even still qualify for Apple Care, even Apple Care+), but they come at a significant cost reduction to buying new (especially if you buy a generation or two back). The only real downside is that support might end for them sooner than they do for a new machine.
I've been hit and miss with refurb replacements. I think in the last handful of years they must have improved the requirements on what they'll use as a refurb, because I've had to exchange iPhones and iPads in the past (never Macs for some reason) and have gotten some real doozies in exchange as far as cosmetics. It's how I learned early on that getting in the return/exchange cycle with any given device, even one not from Apple, can be maddening.
I'll just give the example I remember best: my iPad 3 with Retina Display back in 2012. My first unit had a dead pixel or two that I didn't notice until about a week into using it. I returned it and got a refurb with 3 dead pixels. I returned that and got one with a perfect screen but a visible scratch in the glass on one corner in the bezel area. I figured after 3 exchanges I was finally at least free of dead pixels, so I just didn't worry about the scratch and carried on. I had similar issues with my iPhone 4 back in 2010--dead pixels, damaged antenna bands right out of the box, a wifi antenna that wasn't working, etc. Same deal as with my iPad 3--a zillion trips to the Genius bar and finally settled on a unit that had no functional problems but clearly was not treated well in manufacturing.
Either my standards are too high, or the cosmetic standards for Apple's refurbs are too low, but I've never had super great luck in this regard. I usually try to stick with my original unit as long as it's functioning correctly and not falling apart out of the box.