I have had some involvement in very similar rifle shooting and there is obviously crossovers with pistol shooting. Honestly the fact that you consider those glasses a “gray area” of cheating made me snort laugh. No one in that sport would consider that even close to cheating. Full stop. I’m not trying to be rude but you clearly know nothing about this sport. Those glasses are ubiquitous in many types of competitive shooting at this level especially air pistol/rifle.
In fact if you think this is cheating you need to see what rifle shooters wear because those rules allow way more gear (including your “grey area” glasses).
Also you don’t need something tied to your finger to feel your heart rate…You can clearly see your heart rate in your sights (yes, even irons).It could be a counter balance if it was measured perfectly but that’s risky because if her stance changed at all it could pull her off. I’m honestly surprised her coaches let her risk having that thing at all. It looks like a liability to me.
Edit: I just went back and looked a d there’s no way that things a counter weight. It would need to be close to the weight of that pistol to be helpful. Air pistols are light but they aren’t “stuffy” light.