Yes, the aspect that you need to test things on many mobile networks does become easier when you can easily switch the SIM - that alone makes it kinda essential

Yes, the aspect that you need to test things on many mobile networks does become easier when you can easily switch the SIM - that alone makes it kinda essential - unless you have multiple devices for each network and there are a lot - more so if you factor in roaming. That and nobody ever advertises how many times you can swap a sim and the socket pins won't break. Kinda makes you wonder how many times you can swap a sim before the socket suffers failure of some form, from wear and tear. I've certainly had a fair few break over my lifetime and that's from light usage. Though getting full sized sim cards is becoming harder these days I have noticed - even the precut multi sim that you push out the sim for the size and the aspect that the last phone I saw that would take a full sized (credit card sized) sim form factor was two decades ago.