The presence of the metal body in the smartphone is both advantage and disadvantage - it all depends on the priorities of the consumer. Some like the feeling of strength and solidity, which gives the metal case. Some confuses a slippery surface and the increased weight of the device.
The high end smartphone Sony in 2015 should try metal case which will produce Foxconn unit. Actually, in the production of smartphones themselves with metal frame will be also engaged in Foxconn company , located in northern China.