i actually like that trade for you. You're roling the dice a bit with Harvin, but Ellington has been very good this season and the Cardinals are looking like the best team in that division right now (which always helps fantasy numbers).
Big thing is you'll be weak at receiver until Josh Gordon returns. Plus, you have Michael Floyd and Ellington, so if Arizona starts to struggle, you're team will too. But right now Arizona is playing great, and as long as you can find a filler WR2-3 until Gordon gets back, it's good.