I'm not sure if my experience with this device is normal, but so far mine has managed to make all the saves on a memory card invisible, no device I have can see them, yet they take up space on the card.
The compression/decompression/transfer of saves seems broken. The software ALWAYS compresses the saves when they're placed on the drive. Upon transferring the saves back to the Official Memory Card, the saves become corrupted.
Being able to transfer the saves uncompressed would have been useful.
I have lost an entire cards worth of saves and half of the space and saves on another card. Can't say I'd advise anyone to purchase this.
Hopefully this is just my experience.