I got this one https://www.amazon.com/gp/product/B06WVCWY41/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1
edit: I just realized they're almost exactly the same :rofl:
A window should pop up on your computer asking you to format. Select cancel or else your 3ds will brick. If it doesn't pop up and you don't have a drive letter assigned, your sd reader is incompatible.