assume tor does have zero day exploits right now. Also assume that an adversary therefor knows which celltower you are connecting to and can trace you to an area as small as 1 block. So if you use a mobile hotspot with tails in the middle of nowhere in your mansion then assume you are as unsafe as someone using their home wifi.

So when using your mobile hotspot you want to use it in a high density area (appartment building) or use it at a different location every time just make sure you are not recorded and also your car isn't. So best not drive to a deserted place in the middle of the night because the chances of your car being the only car in that place at that time and being recorded by someones security camera is extremely high in this case.

If you do this then an adversary would actually have to use an imsi catcher at the moment you are plugged in to find you just like with a metal detector. You can keep your sessions limited to 5 or 10 minutes and always in a different locations to make this practically impossible.