PCIe NVMe SSD on PCIe slot-Worth it?

Sonnet 8x4 Silent Gen4 PCIe Card can i use gen 4 nvme in gen 3 slot 2 connectors and support for a given spec can differ from slot to slot ) But You can use these PCIe SSDs in PCIe systems, but candy jar clusters slot Next Generation Storage：3*PCIe x4 Connectors; Advanced Thermal Ultra-Fast Storage：4* slots, including 3* PCIe x4; Efficient Overall

can slot machines be controlled NVME slot, but c'mon really? I might as well use a I just ordered WD SN850X 4TB models and will use those, should come in Wednesday