I'm all for freeing Mickey, but I don't think it makes sense to play him this year.
On paper he seems like he might be a good match up against Atlanta because he's quick for a big man and could go Millsap or Horford problems.
The issue is that he's extremely young, and prone to mistakes, when every possession counts in the playoffs mistakes can't be tolerated, and with the way Atlanta moves off the ball the Hawks put a ton of pressure on opponents.
All season I would have preferred Mickey to Zeller, but now that the regular season is over and Mickey didn't play much Zeller is clearly a better option. Granted, I think Brad will focus on small ball lineups and Zeller/Mickey won't see much court time anyway.