Depending on the size of your smartphone, finding a suitable spot to mount the smartphone could be a challenge, and even more so if you intend on using the selfie camera for in-cabin recording, too.
Whether you’re using a 2-in-1 front-and-interior dash cam or one that comes in separate units, the dash cam is built with discreetness in mind. It doesn’t matter if you have a wedge-shaped, a hanging mount, or a cylindrical dash cam, all these are designed to be mounted right on the windshield, behind the rearview mirror, and out of the driver’s line of sight.
The Driver App requires at least the iPhone XS, which is about 5.64” H x 2.79” W - pretty big to be discreet regardless of where you have it mounted. And don’t forget, if you’re using both the front and selfie cameras, you need to find that perfect angle that can see the road ahead and in-cabin activity without obstructing your view. Unlike dashcams, where the front camera and the IR camera can be rotated separately to get that perfect angle.