9to5Mac posted a review on the OWC Accelsior 4M2 PCIe SSD
A quote from the article:
One of the great things about the Mac Pro, and the primary reason why Ive been anticipating it so much, is its ability to accommodate PCIe expansion. With the Mac Pro we finally have a modern Mac that can be expanded, not only via external Thunderbolt 3 peripherals, but via internal PCIe cards like the OWC Accelsior 4M2 PCIe SSD.OWC Accelsior 4M2 PCIe SSD Review
OWCs newest Mac Pro-friendly accessory allows users to add a significant amount of fast solid state storage to their machines in just a few minutes.