You'd basically be trading a first for a 30-game rental-- and that assumes that he stays healthy for those 30 games. A first has better value long-term, unless (a) you're an immediate contender who thinks Evans will put you over the top (that'd give you 40ish games and perhaps an Evans more willing to re-sign) and (b) you believe in Evans's ability to stay on a court and contribute to a winning basketball team.