I was running a few tests in Chrome dev tools, overriding the useragent to:

Mozilla/5.0 (Linux; U; Android 2.3.6; en-us; Nexus S Build/GRK39F) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1

.. and agent.device returns

Device { family: 'Samsung undefined$2', major: 'Nexus S', minor: '0', patch: '0' }

NB. Useragent source: Chrome Dev Tools 'Android (2.3) Browser - Nexus S'.