Obviously the inventors of this stuff have realized that no amount of scrubbing will clean grout, so painting it becomes the next best option. The pen is like a big white highlighter with a white paint that readily covers the grout.
How to restore dirty tile grout! (Because crawling around on the bathroom floor with a toothbrush is my idea of fun!) May give this product a try if the cleaners don't do it...trying to find something that protects or seals worth a damn going forward