My previous phone holder rotated about a ball joint so I could set the phone in either portrait or landscape, with a flick of the wrist.
With this design, once I have the phone in-place there is approximately 10deg of rotation side-to-side. If I try to rotate counterclockwise beyond that point, the threads start to loosen, if I go clockwise I start to twist the bendy-arm.
Luckily this design takes advantage of standard 1/4-20 hardware, so what I might try next is buy a ball-joint like one you would see on a camera tripod, and mount that between the arm and the phone holder.
All this being said, if you don’t need to rotate your phone and you want your phone to be secure in one orientation through some rugged use, then this will treat you well. For instance, if you’re driving your car on a track and you want to film a lap with your phone, then this will be great, set it and forget it. Or if you are off-roading, this will be great.
I am trying to build a good phone holder for road trips, where I can to rotate the screen vertically for some apps and horizontally for others…. So, for me, this is a good start, but it lacks some functionality straight out of the box.