In addition, the above link sends people to an associate page for my e-book, so I can double check the number of visitors and also know if any sales were generated. Now that's a powerful weapon. Imagine if you wanted to know which headline grabs the viewers attention best. You could guess by changes in the number of sales when you change the headline. Or you could test each headline, make small changes and test again.
Visitors cost money.
Either direct cash if you use pay per click search engines, or indirect cash through time and effort spent marketing. You've just doubled your sales, doubled your cashflow and doubled your profits. Test, test, test. Then test some more. All done in seconds.