Thanks for the prompt reply!

Just one quick clarification: On Macs, you have both a Control key and a so-called Command key. The Command key is used for system level and application menu shortcuts, for instance:

Command-W: close window

Command-H: hide application

Command-+: zoom into document

Since Tabs Outliner won't use any Command based shortcuts on Mac, it would probably be best to whitelist any shortcut involving the Command key.

If I were you, I would put a litte note on the "Upgrade to Paid Mode" page that the actual price depends on fees and taxes and that it should be in the $15-20 range. A lot of people feel alienated if they are asked to click on a buy button without having any idea at all what the price will be. They might even think you intentionally don't tell them the price to make them move ahead in the purchasing process, which would be a bit shady. If you put that little note there, before they have to click the buy button, they both get a general idea of what the price will be and they will also understand that there is a perfectly innocent explanation for why you don't show the actual price.

Since you also brought up Chrome SignIn, there is another reason why people don't sign in, besides not wanting to: Tabs Outliner works well with other browsers that are compatible with Chrome extensions, but those naturally don't allow you to "sign into Chrome". I, for instance, use Tabs Outliner with Opera and am therefore sadly prevented from purchasing it. Sure, Opera does not have a huge market share, but the kind of people who use a non-mainstream browser are much more likely to be the kind of power user who would pay $20 for a browser extension.

Furthermore, Mozilla recently announced that Firefox will support Chrome extensions soon. If you can make (most of) the paid features work without having to be signed into Chrome, you can significantly increase your customer base.