I never told anyone to carry a decompression needle lol...it came in an ankle kit I bought. I also identified my level of medical training and mentioned what was important for nonmedical folks to have (quickclot/Celox, TQs, chest seals, gauze, etc). None of these things are too difficult to learn how to use for someone willing to watch a few videos.
Right, I don't carry any of that stuff as EDC, but I should toss my stethoscope in the car. The BP cuff and pulse ox provide data but I wouldn't say that they are a priority for my med bag.
I'd do what they did before we had stethoscopes, put my ear on their chest and listen for breath sounds, also observe for a deviated trachea. Not ideal I know. And you are right, I've never used a decompression needle or placed a chest tube but I understand the concept. I would be very hesitant to use the decomp needle to be honest.
Or level of non training with a decompression needle...