I am using the 64 GB card in a Galaxy Note II phone and have had the card working perfectly from March to October. The speeds were fast and it always worked flawlessly.Then one day I decided to protect my data prior to going to Europe by encryping the card in the phone.The encryption process went properly and took about 3 hours (as my card was filled with about 18 gb of mostly image files).However, the phone then slowed down considerably and it took up to 10 second to decrypt the card every time I woke the phone up the screen. Needless to say I didn't like that and decided to return the card back to decrypted state. I did the procedure of decrypting it back and when it was done, the card became urneadable. Attempting to format it in the phone as well as in the computer with various utilities programs did not help. The card showed those old folders being present despite multiple formats but I could neither access the files nor permanent write to the card. (The phone could save pictures to the card while it's powered on but after restaring the phone, the newly taken pictures were gone).I contacted SanDisk who graciously exchange the card which now work great again. I give the card 4 stars just because I don't know whether the experienced problem was due to the card or the phone. The SanDisk has shown itself to have great customer service and I really appreciate them exchanging the card. I will definitely not encrypt it anymore. When card works, it works super fast and reliably.