There’s a “gotcha” with that device. From the second review for it:
Each of the 4 m.2 pcnvme slots have only 1 pci express lane. This means that the drive in the slot is limited to 8Gbit transfer speeds.
If you populate all 4 slots and use the included softraid software you will be able to reach the announced speed of 2600Mbyte/sec speed but with fewer drives you will loose out on speed.
So if you want speed you’ve got to commit softraid 0 and to 4 NVMes off the bat, which in turn makes incremental upgrading not really possible.