The fake-to-third, throw-to-first pickoff move now would be considered a balk. Baseball's Playing Rules Committee voted last year to outlaw the trick move, but the union vetoed that change temporarily, pending further discussion. MLB has the ability to implement that change unilaterally for this season, but is hopeful the players will agree to the new rule so it can be implemented jointly, sources said.
I don't think the move is bad per se, but it never works. No one ever throws over to third on a runners-at-the-corners setup; I can't recall a pickoff attempt by a pitcher at third. Occasionally, a catcher will throw down to third to try and catch a runner getting too generous a lead, but any move of a pitcher to third is merely a preamble to a move to first, and everyone in the yard knows it.
MLB has said "get that bovine excrement out of here." Next stop, cracking down on the bluffs to second that rarely get called, but that does have a use from time to time.