Up until a few days ago I would have given this app a 4 star rating. It was easy to use, gave you a good number of hints and chances to correct wrong answers, no ads, saved your progress, had multiple difficulty levels, kept your best times for each level, and highlighted same numbers across the rows/columns. It stopped working about three days ago. It won’t let me sign in or even play as a guest. Customer Support is a joke. No one responded to any of my sent emails, even before the app stopped working (several months back I lost my fastest time and emailed support a few times about recovering it with zero responses). I have deleted and redownloaded the app several times, turned my phone off and on, and tried accessing it on wifi and data to no avail. This is very frustrating, I have lost all my progress and will be looking for a different, more reliable app to use.

All good, but I would like it better if you could stay on the board after winning or losing. I like to analyze my win/loss. It flips immediately to the next screen and you can’t go back.