The machines were set to be activated on Oct. 1 in front of the Parco department store in Shibuya.
There are hardware and software requirements to use the machine. Customers need a device running Android 4.0 and up with NFC support. The phone is placed on a tray -- and it looks like you're not going to be putting a tablet there, and perhaps not even a phablet -- and NFC takes care of the transfer of the software to the device.
As you might expect, there might be (should be) some confusion associated with the rollout, so Google employees, dressed in white, are set to assist users when the machines are first switched on.
It's unclear what recourse users would have if the transfer didn't work, but considering that you can usually go into the Play Store on your phone and download or redownload at will, there shouldn't be an issue there.