I'd think what you want cost being the regulator.
into from the net:
Late 2014 was the first Mac mini to support Apple’s blade solid state drives, but it’s extremely limited internal space required a unique solution in order to connect the drive to the logic board. Rather than a 12+16 pin PCIe connector on the logic board where the SSD would connect directly, the Mac mini positioned the SSD on the rear of the plastic hard drive carrier, off to the side of the board, and required a flex cable to connect the SSD.
The flex cable has the 12+16 pin female connector on one side and a female 40 pin mezzanine connector which attaches to the 40 pin male connector on the motherboard. This was the first and last time Apple used this smaller connector for PCIe connections in any of their product lines.
PCIe connector on the Late 2014 Mac mini
The connector is present on the board regardless of which storage configuration was initially ordered, so it’s possible to add a PCIe SSD to all Late 2014 Mac minis. If the Mac mini wasn’t originally configured with a Fusion Drive or standalone SSD from the factory, the flex cable will need to be purchased in order to add an SSD afterwards.
The Mac mini motherboard only supports a PCIe 2.0 x2 interface, but does support an upgrade to NVMe SSDs, but like the 21.5″ iMac, the speed increase is a modest 10-15% due to the two channel PCIe bottleneck.