I think I read somewhere that GI’s would use this against the enemy (I think this was about the European theater). The Germans had learned to listen for the sound of the empty clip. The GI’s would drop or otherwise hit the clip to mimic the sound, while having a full clip in the M-1. Bad news for the German who then stuck his head up.
The “ping” is not that loud so you have to be fairly close to hear it and GIs generally are not alone. Moving to get the “one” places you in the sights of the others.
The clip makes more noise bouncing on the cement - if you're on a range - than the system does as it ejects the clip.
I like shooting my Garand and have been on the range a few times with a number of others. While you can hear your own weapon's “ping” and a table or two to either side it's hard to hear the “ping” four or five tables over.