I think you would want two devices--one for the rear view mirror job, and the other being your actual device.
You have to go the app store and get the free Hopkins app installed on your device. You could get that on more than one of your devices I suppose. You get your device to select the Hopkins wifi so it is on that, and they give you a password. You only have to use the password the first time. Your device can only be on one hotspot at a time and now you are on that.
I don't know the technology for wifi boosters for how they boost a particular signal.
I use the old iPad no longer in use for the mirror display, but I have a smart cell phone that is for "real" stuff. (Except it is not to be used when on the road of course.) So no conflict with hot spots for the cell phone. It can do data on the carrier's that you pay for, or else free hotspots if any around.