Tweenx.setField for composed Sprites in flash

[postite]

would it be a performance issue if we use

     Reflect.setProperty( o, key, value );
    instead of 
            untyped o[ key ] = value;

for flash target ?

because i use something like this

  class View {
  #if (flash || openfl)

    /**
    native flash sprite representing this view in the display list
    */
    public var sprite(default, null):Sprite;

#elseif js

    /**
    native html element representing this view in the DOM
    */
    public var element(default, null):Element;
            #end
            function get_x():Float {#if js return Std.parseInt(element.style.left);#else  return sprite.x;#end }
            function set_x(value:Float):Float
            {


#if element.style.left=value+"px"; return Std.parseInt(element.style.left);#else
return x = sprite.x=value;
#end

}
}

...

     TweenX.to (myView,{x:200}.time(1);

arrayAccess doesn't work in that case

thanks