I would say your probably better off investing in just nail art tools for seven dollars. These nail art pens aren't very good. They will break on you, splatter nail polish all over your nail, smudge, or ruin the previous nail polish you put on.
If you are however interested in buying a nail art pen I know Milano has one for about the same price. Sephora has a great one too, at about ten dollars. I would just get nail art tools though. You can get nail dotters (plastic sticks with metal balls attatched to the end that you dip in nail polish to make various sized dots) at amazon, a set of five for around five dollars. Or some nice nail strippers from kiss that come in a pack of three and are around about seven dollars. May I also suggest buying nail art stickers? They're super cheap. You can buy them at your local drugstore or I know sephora has them too.