It’s Definitely the best functioning 15 puzzle on the AppStore, but it used to have a timer at the top and would record your best time and keep up with your progress. Now there is no timer, and when it shows the time after you solve the puzzle, the best time changes to whatever time you got that solve and not your actual best. The puzzle itself Functions well, but with the annoying ads, and now the timer stuff, The other aspects of the app are kinda lacking.