For 49¢, I'll buy 10!
The 2014 is actually easier to upgrade with NVMe SSD than the 2012 model with SATA SSD. BTW, it's probably a bit easier to upgrade the 2014 model with just the hard drive in it, but the Fusion one also appears to be easy to upgrade.
The blade drive port is extremely easy to access. Literally a 5 minute job. You do NOT need to move the logic board, but you need to have the appropriate screwdriver and buy the appropriate SSD adapter. The adapters are different depending upon if it's a hard drive only model vs. a Fusion model.
The key here is you don't actually touch the hard drive. Just leave it there.
Here's my upgraded hard-drive only model:
My eBay Mac mini arrived today, and to my surprise, inside of it it was absolutely pristine. It looks like the seller must have cleaned it before sending it. I had already ordered the PUSOKEI branded NVME adapter from Amazon Canada, simply because it was cheaper than the Sintek. Like half the...
forums.macrumors.com
Just be aware that the machine needs to have upgraded with a more recent OS, to provide NVMe SSD compatibility. This has to be done before the SSD is installed.