It only scans the outside of the letter, not the contents. I'm not sure I follow how that's enough to steal a credit card number or other sensitive information in the mail.
Regardless, it is a great service to sign up for. You do get it automatically if you have other accounts or used too. I had a few people sign up for it at work.
the reason I started was we had a disappearing mail issue in my neighborhood that was eventually solved. plus its good to know when stuff you are expecting actually arrived. since I order a bit online having the packages listed is a great feature but they do not photo scan those. you can set delivery instructions for some
its free, its useful, and while it does have a security issue along with nearly every service the post office offers it hurts you not for using it.
in a day an age where we have privacy issues one of the biggest is proving who you are to agencies that have a real effect on your life and others. so we need to solve the ID issue as well.