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> The Silicone sponge is perfectly hygienic. Its completely airy ("open-cell") structure does not keep dirt or bacteria, is easily washable and dries fast. Silicone is perfectly anti-microbial, no dirt adheres to it.

This sounds like a dubious claim. I've seen dirty sponges with fungus and all sorts growing on them, why should this be any different?

Also what about mineral buildup from hard water? Surely the microbes can adhere to that too.

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They say a sponge has an estimated effective lifespan of two months, so I don’t think hard water should cause issues over that timespan.

Also: the solubility of calcium carbonate goes down with increased temperature. Which is why your kettle gets covered in scale, while your toilet and sink generally don't.

Since the brushing process happens at a roughly constant temperature, this is going to behave more like a sink than any appliance that heats cold water and puts out hot.

I wouldn't worry about it if I were to try this. The fact that sponges turn gross in short order would be much higher up my list of reasons to be concerned.

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