'To' Pronounced to as in Tow truck, not 'two' You are the first person to have ever asked this
To as in toishi (sharpening stone). This is a custom formulation that I had made specifically to fill what I perceived as a gap in the Nubatama lineup.
The 2k Bamboo is an expensive stone - superb for a baseline for natural stones as a followup.
The Black 2k Ume is a superb stone much like the green brick but a bit softer, but still pricey.
The Speckled 2k Ume is a regular sized stone and more general purpose with hardness characteristics much like the
Ume speckled medium hardness 1k - which is ideal for most knife users needs at an affordable price. When they come in, I suspect they will be very popular.