(July 13, 2018)
The 2014/2015 Mac Mini is still, in 2018, the "current" Mac Mini model, and its biggest problem is the great difficulty to upgrade the device. While it is impossible to replace the memory it is possible to replace the hard drive, so long as you bought the upgradeable Mac Mini. Namely the version sold with an HDD. The other, with PCIe SSD, does not support upgrading the disk. You can save some money by purchasing the HDD version and upgrading to SSD on your own, however performance is higher with the PCIe version. The videos attached to this post document the overly unnecessarily difficult process for upgrading such Mac Mini's to have an SSD. You have to remove everything just to swap the disk? And you can't change the memory? The Intel NUC is in the same class of machine, and does not require this kind of over-the-top surgery.