I've been using this dotting tool for about months now and as a nail artist it gets used a lot for various things not just dotting. I will admit that it doesn't really work for lines, if you want lines I'd buy a striping brush but both ends of this are great for getting different sized dots.
I don't know why all the other comments are complaining that it doesn't dip into a nail polish bottle because obviously that's not what you're supposed to do with it. the instructions say to tip some polish onto a cloth, but to save the mess I just dip the dotting tool into the brush in the nail varnish. Just pull out the lid like you and dip the tool into the brush covered in nail polish and then put the lid back in, make the dot on your nail and repeat.