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If it provided a feature to automatically block incoming dick pics, which Google claims it’s for, was fully local, and only scanned incoming messages, not my own gallery, which is what Google claims, I would likely find it useful. There is nothing wrong with the idea in general.
At the very least it wastes your battery
Again, if it’s an optional feature that you can choose to turn on or off, there is nothing wrong with that.
One could think so, but no cybersecurity experts share such opinion to my knowledge.