I think the SB Touch App is non P2P as there is no/limited local storage. Spotify Premium is required.
Triode's Server Based plugin is similar / Better , as it has more (menu) options, and allows you to stream spotify to older / software based clients .. (not just touch and radio) (non p2p also as it uses the web api )
More Details here ...
http://forums.slimdevices.com/showthread.php?96330-What-steps-do-I-take-to-download-and-install-Triode-s-Spotify-plug-in