No commas, apostrophes or hyphens please. The most important job of your title and sub-title is to help readers find you through search results.
Yes, you want that title to grab the browsing reader you are hoping will buy your book, BUT for them to see that title they need to have your book come up in front of them.
In a book shop these potential buyers browse books on shelves and books on the middle shelves, closer to eye height, will get the most views and a catchy title will grab their eye, and their desire to find out more about your book. But if your book is on the bottom shelf your catchy title won’t do much for you, Few of those bookshop browsers will ever see it.
Discoverability is everything!
Coming up well in online searches is the same. You must get your book cover with your appealing title in front of that reader browsing the digital bookshelves on Amazon, Smashwords or wherever. That is your goal.
Great reviews etc are the cream, early promo selling your book to fans and friends will help place you higher on searches that find your book, but if your title is not easy to find because buyers don’t type in the title correctly, becasue they leave out the apostrophe or comma in the title, you still wont come up near the top of their search results.