Silverstone ECM20
This expansion card has dual M.2 ports to support two SSDs simultaneously—one M key port operating at PCI-E x4 interface and one B key port operating at SATA interface.
No driver is required. You only need to plug it into the PCI slot of your motherboard. Connect it to the motherboard with a SATA 7-pin cable (not included) if you need to use the B key port.
Converts one M.2 port (M key) into one PCI-E x4 interface
Converts a second M.2 port (B key) into SATA interface
PCI Express X4 interface
SATA 7 pin connector to motherboard
Pros: allows you to add one NVME M.2 SSD and another SATA M.2 SSD to you system and doesn't cost a lot. Short bracket included if you have small chassis, mounts and screws are included for two drives.
Cons: You can only use drives as mentioned in "Pros" above, meaning you cannot use two of the same type of drives together. And if you use just one it needs to go into specific socket, i.e. NVME SSD will work only in "M-key", and SATA drive will only work in "B-key" and you will have to use SATA cable. Since you must use SATA cable when using SATA type M.2 SSD, then probably cable should have been included, but again, this is fairly inexpensive unit so this can be forgiven.
Overall Review: If your motherboard does not have M.2 slot or you need additional M.2 sockets to add to your system, this is a very good and rather inexpensive addition. Just know the limitations. I used it to add SATA3 M.2 drive for extra storage to my computer using Widows 10 and it works well so far.