I am using the Fiio X5 and my current 64 GB SD card is full. My library is now bigger than 150 GB and this Sandisk 128 GB card had a price drop to $100 and with free shipping, it was a no-brainer to get it to accommodate all my music files. It worked as advertised and speed can be further improved but then I am limited by the read speed of my player X5. Overall, a good product with the big memory space which filled my needs. Recommended to buy again if there is a discounted price for this card. Else get 2 x 64 GB card, which is still cheaper than a 128 GB SD card.