MZ-JPU256T/0A6 PCIe blade is fit to Mac Mini late 2014?

Lets first talk about what you'll need in order to install an Apple Custom SSD.

To start with your system needs to have the lower bay vacant (the one you see from the bottom cover) to install the second drive (SSD). You might have a traditional HD model which is using the upper bay or you could have a Fusion Drive setup which you want to upgrade the blade SSD to a larger unit or you could have a blade SSD only model.

So assuming you don't have the needed cable to install the SSD as it's not offered in the traditional drive model you'll need to add it first flowing this IFIXIT guide: Mac Mini Late 2014 PCIe SSD Cable Replacement Getting the cable alone is not easy. The only way I've found it is already mounted into the carrier Apple P/N 076-00040.

As for the custom SSD: There are two versions of the Samsung custom SSD for Apple PCIe x2 and a PCI x4. In addition the newer 4 lane version is very hard to find on the open market and likewise very expensive. Here is the workable PCIe x2 SSD's IFIXIT offers.

You'll be able to get a 3rd party unit from OWC soon as you can see here: SSD Flash Storage Upgrades for Mac Mini