It's an aluminum micro SD card adapter that fits 100% within your Surface Book /Surface book 2 and 3 13.5" & 15" without any awkward protrusions.
You can place a micro SD card into this adapter and gain up to 512GB of extra storage space for your computer.
For example, if you place a 64GB (~512GB) micro SD card into your Ninja Stealth Drive, then you will get 64GB (~512GB) of extra disk space on your Surface Book / Surface Book 2 13.5". & 15" The read and write speed for each brand of micro SD card varies, you can pick your favorite brand and use it with your Ninja Stealth Drive.
If you need a memory card solution, please take a look: https://www.ebay.com.au/itm/392278111521