I really like this app, but I do have some gripes.Major gripe.I don’t like the interface design with tools and numbers. It seems very non intuitive to me. I would like the buttons to be divided between actions, modes and objects.Objects would be the numbers 1-9, the 19 number pair, X and the colors (these can all be used to fill any selected area).Actions would be trash, undo, redo, and erase selected objects (the current erase is modal and only erases numbers).Modes would be limited to the three number placements (one of the three buttons should always be selected) and the button for for multiple area select which should toggle between on and off and be independent of the number modes.Minor gripes.At one point in the first puzzle I had filled in all the 8’s and accidentally turned one of the eights to a seven which was red, but because the eight at the bottom was still grayed out I couldn’t press it to restore. I finally realized that that I could use undo (which I hadn’t used before that) to fix it.One and nine at the bottom was grayed out but the 19 button wasn’t.The shifting background makes me think my eyes are going bad and the other colors schemes are horrible.Kudos.I only looked at the first hint on the first puzzle, but it was so good compared to any other hint I have gotten in any other sudoku app that it overcomes my gripes and so gets a 5 out 5 rating.