DSF

Wifi uses higher frequencies which will be more susceptible to shielding but it all depends on the location of the transmitter and how much of the signal comes from reflections and not direct line of sight. NFC uses EM radiation for communication and not RF radiation and is only point to point so adding a sheet of aluminium into the path may reduce this signal as well. The insert is not grounded so the real effect may be quite small.

When contactless payments are the norm, maybe the aluminium inserts will reveal a problem? iPhone cases are a mixture of metal and plastic for technical reasons, so introducing a layer of metal over the plastic may cause problems?

"Finally, a contactless card has to be used in a specific way to work. That means it can only be a few centimetres away from the card reader and not near any metal objects, like keys and mobile phones, or indeed any other contactless card."

People complaining about aluminium cases and NFC:

http://forums.androidcentral.com/samsun ... no-go.html