I don't have a chair that this will work on, but I liked the idea of it and plan to use it when I travel to see my parents. They have a high chair we use, however it is a wooden one from when my youngest brother was a baby (he is now almost 22) and my poor daughter slides around in it if we don't line it with towels and use extra long towels to die her down. This will help hold her still in the high chair and I can't wait to try it out!
I also saw a "5 point harness" type travel chair to turn any chair into a high chair and wanted to make one of these as well. The problem was I couldn't find a free tutorial for one. Granted I didn't search for too long before I decided to just come up with my own. I was inspired by this version and this video, and just let my creative juices flow.
Here is what mine looks like (again, minus the baby who is napping).
Here is the front
And the back
The first travel chair took me about 2 nap times to complete. The second took about 3 to complete after I had figured out how I was going to make it. I can't wait to try them out now that they are finished.