The sound of the Full Circle heavily depends on the rotational orientation. Not so with the Yamahiko.
But the main reason why I changed is durability.
On the Full Circle there are four piezo crystals in the corners of a square inside the adjuster disk. These piezo crystal take float the full pressure of the bridge leg. Over the years the crystals can break due to the heavy pressure or by impact on the bridge by bumping the bass while carrying.
The Yamahiko has the piezo inside the axis and it is mainly sensitive to bending. No force on it, so it can live for a really long time (like a bridge wing pickup that gets minimal pressure compared to a bridge foot pickup).
But I like the sound also a bit better than the Full Circle.
As long as the thread is not damaged, a used Yamahiko is fine.