I absolutely adore this, though I don’t fully understand how it works. Notoriously the thing keeping these from being useful is the lack of a meaningful way of counting rounds. These round counters can really just count how many times you’ve pulled the trigger (or count how many times a sensor felt recoil, or whatever mechanism the designer decided on) since you’ve inserted a magazine, so as soon as you get a jam or switch mags before completing the count (or what have you), the counter is wrong. I saw the thumbnail for a youtube video explaining exactly that one in that picture, but I’ve yet to click on it.