Difference between Newtype and TaggedType

01.source.scala

-- package.scala --
object Booter extends TaggedType[Int]
  type Booter = Booter.Type

implicit class StepOps(val __v:Int) {
  def next:Step = Step @@ (__v + 1)
  def +(v2:Int):Step = Step @@ (__v + v2)
}

object Step extends NewType[Int, StepOps]
type Step = Step.NewType

-- Chocker.scala -- 

// Boxing operations and boilerplate for booter0 will be optimized by JIT,
// but I saw nowhere information that it can move Object to primitive

class Choker {
  val step0:Step = Step(5)
  val booter0:Booter = Booter(6)
}

02.Chocker.bytecode

public class Choker {
  public java.lang.Object step0();
    Code:
       0: aload_0
       1: getfield      #31                 // Field step0:Ljava/lang/Object;
       4: areturn

  public int booter0();
    Code:
       0: aload_0
       1: getfield      #36                 // Field booter0:I
       4: ireturn

  public Choker();
    Code:
       0: aload_0
       1: invokespecial #40                 // Method java/lang/Object."<init>":()V
       4: aload_0
       5: getstatic     #44                 // Field package$Step$.MODULE$:L/package$Step$;
       8: iconst_5
       9: invokestatic  #50                 // Method scala/runtime/BoxesRunTime.boxToInteger:(I)Ljava/lang/Integer;
      12: getstatic     #53                 // Field supertagged/package$Tagger$.MODULE$:Lsupertagged/package$Tagger$;
      15: invokevirtual #57                 // Method supertagged/package$Tagger$.baseRaw:()Lsupertagged/package$Tagger;
      18: invokevirtual #61                 // Method package$Step$.apply:(Ljava/lang/Object;Lsupertagged/package$Tagger;)Ljava/lang/Object;
      21: putfield      #31                 // Field step0:Ljava/lang/Object;
      24: aload_0
      25: getstatic     #64                 // Field package$Booter$.MODULE$:Lpackage$Booter$;
      28: bipush        6
      30: invokestatic  #50                 // Method scala/runtime/BoxesRunTime.boxToInteger:(I)Ljava/lang/Integer;
      33: getstatic     #53                 // Field supertagged/package$Tagger$.MODULE$:Lsupertagged/package$Tagger$;
      36: invokevirtual #57                 // Method supertagged/package$Tagger$.baseRaw:()Lsupertagged/package$Tagger;
      39: invokevirtual #65                 // Method package$Booter$.apply:(Ljava/lang/Object;Lsupertagged/package$Tagger;)Ljava/lang/Object;
      42: invokestatic  #69                 // Method scala/runtime/BoxesRunTime.unboxToInt:(Ljava/lang/Object;)I
      45: putfield      #36                 // Field booter0:I
      48: return
}