They are far more noticeable and less suited for covert tracking than AirTags: they need far more power, reducing the time of autonomous work, they are significantly bigger, they need to be in the coverage area of mobile network.

Also, AirTags look far more innocent, giving a plausible deniability excuse to a potential stalker. Oh, that's where I lost that key, it's on the floor of your car! With specialised tracker that excuse won't work.