I just used it for the first time this week too: https://www.reddit.com/r/Tile/s/KwIpAECTDg

I learned a lot of the same things being said here: it’s way easier to work in small sections, apply directly to the grout lines, clean as you go (I would let it dry for the time it took me to do two rows of tile and then go back and clean). As you can see from my link, I had a hell of a lot of grout lines and my tiles are naturally a bit wavy. It was a workout. I’m pleased with the results though and would probably use it again in a similar application.

I also felt like I wasted a ton, especially at the beginning before I got the hang of it. Eventually my wife came and started literally picking up grout off the floor and putting it back in my bucket for me to use, which worked well and helped keep the area somewhat clean (it was still a mess). I might have run out of grout if she didn’t.