Sudoku game optimized for serious Sudoku players!

OK, so we're not a big developer and you haven't heard of us, but check out our reviews (and these weren't written by our friends):

"Best Sudoku. Best one out there. Great game play."

"Best? Yes it is! I've played my share of sudoku games, and this one tops them"

"Hands down, this is the best sudoku implementation on the iPhone."

"Best Sudoku on any computer. This is the best Sudoku that I have seen for any computing device."

"This is the best sudoku! I love sudoku and I downloaded and paid for a lot of different sudoku games, but this is the only one I kept on my iPhone and the only one I've kept playing. Thanks for doing such an awesome job on this game!"

"Now try the best. Tried/bought numerous 'top-rated' Sudoku apps and they all have something to offer; this is the one I actually play. Wish I would have found this one earlier."

"Great Sudoku for iPhone! The best iPhone Sudoku game there is."

"Wow. Believe the reviews. Sudoku Star is that good."

Platform:
• Universal app for iPhone + iPad + iPad Mini + iPod Touch
• Optimized for iPhone 3.5, 4, 4.7, and 5.5 inch screens
• Optimized UIs for iOS 8 & 7 and iOS 6 & 5

Basics:
• Unlimited number of games, five doubly-graded levels of play
• Symmetric games with unique solutions
• Six built-in color schemes
• Built-in solver
• Autosave and restore of game in progress
• Game stats: wins, best/average times, percentile

Gameplay automation:
• Automatic and manual pencil marks
• Integrated, graduated hint system
• Bookmarks stack for trial-and-error backtracking

Visualization:
• Optional color-coded errors
• Optional color-coded conflicts
• Optional highlighting of selected digits and marks
• Digits done feedback

Great user interface:
• Both digit-first and cell-first entry
• Large, easy-to-read digits
• Unlimited undo and redo, undo to last correct
• No pop-up entry menus covering board
• All key features accessible from main screen
• Optimized to maximize playability

Free version is ad-sponsored but is otherwise the complete, fully-functional app. Paid version removes ads plus on iPhone 5/5S/5C/6/6+ includes an additional row of digit buttons for entering pencil marks without a mode switch.