He answers that before. The device consumes then to much energy.
Beter a mobile wallet that can access the Raspberry PI with web access.
With EnergyCoin we launches a POS wallet but then the POS was on a server. People don't liked it because it is not decentralize and privacy is not guaranteed because you have to  register.
Gaiacoin has a nice concept that you can access your wallet on your home PC with mobile divide.
That concept has great future and in combination with raspberry PI a killer App!