I was fascinated by Joanthan Twingley's use of a steel brush for his drawings in my Sketchbook Skool Stretching klass. I finally broke down and got one from Amazon. 

Here is my first portrait using it. I love the lack of control it gives you - yet, you can make very thin and thick lines with it. Plus, the ink splatters are great!

And another Sktchy portrait - 

What do you think? Have you ever tried using a steel brush?