I don't advise anyone on using a handheld mobile, especially with a mag mounted antenna. And for a lot of reasons...
Mag mounts are not typically covered by insurance policies, they mar the surface they're on, most handhelds end up just lying on the seat ready to become flying bricks in the event of a crash, most handhelds don't work very well in a metro areas with an external antenna (intermod), and the list goes on.
If this is for temporary use in a rental car, and the necessary precautions are taken, fine. If this is your daily driver, there are much better choices, and in most cases less expensive ones too.