It feels sturdy (heavy) and well made and the phone clamp and scope clamp seems good, they have "soft" surfaces so should not mark the rifle scope. It will fit scopes from 37 to 45mm diameter.
Its adjustable and even has markings on the side. Once fitted to the scope it also feels very secure and does not move about.
It also comes with its own little fabric bag to keep it all safe when not in use, a nice touch. I got mine from Amazon, its marked as "Gosky", but on Amazon it was listed as "Solomark smart phone scope adaptor". Cost £40. Happy with it so far...

https://image.ibb.co/bOtGt5/Air_rifle_camera_mount_may_20172.jpg