He's a free agent, only 24, and played well for Minnesota in 2007-2008, and for Sacramento the last half of 2008-2009. He only had half of a bad season, but he's been hurt, so that may be the reason. He's shown much better shooting ability than any other Knicks SG option, and he gets a good number of steals (1.5 per 36 minutes).
Excluding that lousy half with Minnesota last season, his PER the past two years has been above average. It was 14.6 2007-2008, and 17.2 with Sacramento. His true shooting was 55%. I understand he might be an injury risk, but his numbers when healthy are nothing to sneeze at.