Thanks atwskris, for your review. As you can see, I have updated the description now.
For the redirection to the mobile site, the default is (your site).mobstac.com but you can always override this behaviour, by adding a CNAME say, m.mysite.com to your Domain Record, pointing to (your site).mobstac.com. Get in touch with us (http://getsatisfaction.com/mobstac) if you need help with that.
As for the API key, it is security measure to prevent phishing scams so that only authorized owners of a site can redirect to the mobile version through the plugin.