It is actually inside the passenger side outside mirror ... and it is a shitty antenna because wifi reception sucks most of the time.
Exactly. I’ve seen it change when you fold the mirrors. Some people can’t because it causes it to drop to unusable. Best plan is to have an AP in the house close to the car. But that may not be an option.
Opinions vary - I got similar devices from my ISP and they were garbage. Unless you run a cable to them, they don't give you any faster internet where they are, they just give a stronger wifi signal, which is not the same thing - you'll connect to wifi easily but you might still get crappy speeds if the device can't get a great signal from its buddy devices. Very best bet for your garage/outside is buy a separate basic wifi access point and run a few dollars of ethernet cable connecting it back to your main router/modem.
Running wires to all of your WiFi access points is the best, repeaters are not that great. I installed a Firewall and Cisco 12 port switch in my garage. After I got my Model 3 and had poor WiFi service in the garage; I just plugged in a new access point directly into the switch to solve my poor signal. I use Open Mesh wireless access points.