I didn't remember if I tried physical sim and esim at the same time, but you can do 2 separate companies the same time if both are esim for sure, I think you can do physical and esim also
You won't need to switch between to sims, you can run them both at the same time, you can even assign which sim to use for text messages. So you can have your text messages to thru TMO, your regular line and test the other line for signal. You can also assign which sim is primary for calls. When you run 2 sims you will have 2 signal bars so you can compare easier. When I was testing 2 carriers, I left my regular phone number as primary for a few days then I forwarded my primary to the carrier I was testing. People calling you would use your normal number and if you called back your regular number would show up since you are using it as the primary.