My phone mount is not magnetic. The phone holding part was swapped with a different brand. It has four holding arms. Any phone is secure. Even mine with a heavy duty case cover. The tablet is not meant to be permanent. Later, I may upgrade the radio to an XM capable unit. Plus monitor critical parameters.
The XM module will take little space. Using the battery key off power option will help with installation. A battery to 12V cigarette lighter adapters are available on ebay.