A little slow, and I was inattentive enough to get several pink block alarms. But I did it ngng. 18.
It might be cute if there were a penalty for pink block alarms, something like all the pink cells need to be done again.
Um, this may be a stupid question but I am going to ask anyway: What is a "pink block alarm"?
You can see an example of a pink block alarm by deliberately placing a 7 in a row that already has a 7, or by trying any other obvious impossibility. One might guess that Iron Sudoku includes this feature to help beginners understand the basics. Of course, you don't get that kind of help if you do a Sudoku puzzle on paper.