Those bristles look pretty mean at high magnification, and the sharp tips seem to do the job. The bristles feel stiffer than the 404, (as well as sharper), and the smaller area of bristles certainly concentrates the brushing force.

By far the most successful - if the intent was to polish without damaging severely.

This tool ripped off the toning quickly, and removed hard encrustations almost as fast.

I doubt if this brush can actually "whiz" within the meaning of the term. "Gently" whiz, maybe. "Polish", certainly.

Even under the binocular microscope, at 20x, I cannot discern any scratches which weren't there prior to the "whizzing". (I could have missed some.)

Lest this sound like I am endorsing the use of this brush on coins, I should point out that the polished area looks completely unnatural and "interferred-with" - far more so than simple dipping would cause (I imagine[!] ).

There is  no way on G-d's Earth  that this brush could cause the surface metal of the coin to move. No Sir-eee Bob!