I just coudn't find the right location for my phone, especially while charging. It just isn't handly.
For those that have a magnetic ROKFORM case this is a great add on especially if you can't find a place to stick their own clipon holder.
The diameter for my handbreak is about 29mm, and I had the sides extended down so it doesn't swivel around. Also I added holdes for 2 cableties to secure the whole thing. They even recess in the part which looks really nice.