Earlier quoted context omitted.
Some mechanics charge you $120 literally just to plug in their OBD2 adapter and read the code, so yeah, even if it saves you one diagnostic fee, it's a bargain. Note that Hotz is claiming his readers will do a lot more than the conventional ones you've seen before. Whether or not that's true remains to be seen.
Most auto parts stores will read the codes for you for free. Some will even loan you tools to fix your car. They are in the business of selling parts and are happy to sell you whatever part you need to fix the problem.
You set up Torque into logging mode, clear your codes, turn on the GPS and mapping, and drive away. When your car does "that thing" take a note of the time, then when you get home, go back thru the logs around that time mark, and take a look at all the sensor data, plus any thrown codes. If you know your car, and understand what is going on, it can help you to narrow down the diagnosis.
While a regular code reader (or getting the codes read) will help you by giving you the codes, being able to get the codes, timestamped in a log along with sensor data can go much farther in telling you where a particular problem lies.
While there are other code readers out there that will do this logging and tracking too, they typically cost hundreds or thousands of dollars - well out of the price range of most home mechanics.
There are many other things that Torque can do or be used for (for instance, virtual gauges are a nice feature - you can set up an Android tablet with a cluster of them giving you much more feedback than you can get from your regular dash instrument cluster, and it's cheaper and easier than setting up a bunch of physical gauges on a stock vehicle).