Good find Christiaan.
I see the webpage allows you to 'save' the blend more than once to a series of images - all at the same mix % with a randomised result.
A bit more work, but this would allow you to build a larger sample image as the basis for your texture, thus minimising the dreaded image repeat on larger panels.
The mortar colours don't impress, but if you choose a colour that can easily be colour picked in PS (almost an alpha) you'd be able to replace with your choice of colour from your chosen supplier.
Photoshop here I come....
Designer 2017 SP4