I had a crystal case and it was great case to use with p6. But i didnt buy the imak brand (which supposedly is scratch proof), and i had scratches on mine. A neg. aspect with the crystal case is that removing or wearing it is a bit of a trouble as it is not flexible enough and i ended up breaking mine when i extended it too wide when trying to remove the case without causing any scratch to the phone.
Huawei Ascend P6-U06 (EMUI2.3+KitKat)