Despite the manufacturer's disclaimer, this works beautifully on my cast iron porcelain sink without needing to utilize the second magnet they provide for stainless steel sinks. I bought the white one and it blends well with the white porcelain. It holds a Scotchbrite sponge securely with no modification.
ProsUnobtrusive, provides good air flow around sponge, reasonable price for such good design and production quality.
ConsInstructions do not mention the ability to use it without the unnecessary second magentic block when installing on a porcelain sink-suspect the manufacturer hadn't tried it.