I have a similar setup, with a Samsung Galaxy Tab A (2019) 8" and the Steelie ize car mount kit.
Instead of the typical setup, I decided to stick the large ball on the tablet and to put the small ring on the car. This way, it's a bit more discrete when I remove the tablet. I also added some velcro adhesive where the bottom corners go, to add more stability - I plan to use this at the track and wanted to make sure it does not move.
In terms of apps, Scan My Tesla is fun to use, but in normal driving conditions I don't find it particularly useful. The speed tab is the most useful, but the speed is shown with a decimal place and it updates so fast that it's a little bit distracting.
I typically keep the tablet in the car, with a cable connected to it all the time - I don't yet have a clean cable management solution, but am looking for one of those cables with a 180 degree turn (for example
https://www.amazon.com/BECROWMUS-Smarthone-Andriod-Charging-Samsung/dp/B07FLZVG6J - I need one shipped to Switzerland, let me know if you have any tips). Because the cable is always connected, the USB power goes off when the car goes to sleep (if you don't have your car registered with software that constantly polls it). I set up AutomateIt to automatically unlock the tablet and open ScanMyTesla when USB power is on, and to turn off the screen when the power goes off. This works well, but I have to unplug / replug the ODBLink LX dongle from time to time to get it to connect.
One problem that I hadn't considered is that the Galaxy Tab A tablet does not work well with polarized sunglasses when in landscape mode. When I look at the screen with the sunglasses, the screen appears almost black, and when I bend my head just a little bit, it becomes visible, with the best visibility at 90 degrees (makes for a funny driving position). I tried to add a tempered glass to the screen which improved the situation a little bit, but in the end I found a color filter which fixes the polarization issue entirely (but adds a green tint, which I partially corrected with a Color Calibrator app).