Provides an effectively infinite number of puzzles of a variety of sizes. Controls are good. Ads are present but unintrusive.
Two issues, however. One is that some puzzles are not solvable; specifically 8x10 #111. I’ve double and triple checked this; the puzzle itself is self-contradictory.
The other is that the “pencil” control doesn’t work - the X clears out only “dotted” squats, now solid ones. So using it to roll back after invalidating a guess is useless as a result.