I'm in the middle of finishing a piano key border for my tube-X quilt. I'll try to post a picture when the top is done.
A couple of tips from my experience: you'll want to starch the tube before you cut the triangles and press really well or the bias edges will end up out of control! I used a simple homemade starch of 2 tsps of potato flour/starch to 250 ml of water.
This pattern is a great way to use jelly rolls - I used an Asian fabrics one, with Moda Snow as a background.
Have fun!