I pulled mine the other day to check for something I had seen while driving (actually Tesla car carriers loaded with Model 3s) and realized when I got in the car to run errands in the afternoon that I hadn't replace it. Almost ran back upstairs to get it but was in a time crunch to get something done so didn't. The whole trip out I kept thinking why aren't you carrying your spare card reader with microSD card with you or in the car to prevent this from happening. Of course also was a bit paranoid every time I parked too. While sitting with traffic also stopped with me in the right lane, I witnessed a car fly past all of us in the left lane and straight through a long red light. Could have been a really bad situation given his speed. Was going to hit my save button on TeslaCam but of course remembered no USB device in it. Put it back in the car once I got home. You just never know when it will come in handy.
Excellent idea to carry spare!! Got into a similar anxious situation as well (i.e. no working USB) and wishing I had a spare. Totally worth the extra cost for peace of mind.