Andy's book is extremely helpful in making the SE/E-Trac comparison.
The SE and E-Trac software uses different algorithms to do what they do. They function the same but are, in many respects, different in the way they approach targeting.
What you gain with the computer interface is the ability to import a pattern from someone that has many more years of search and machine experience. You can download it to your machine and use it. Sure you can do that manually with the SE, but when you have to program the pattern Murphy's law will make the effort frustrating.
For instance Andy has a great coin pattern that he has used and refined. All you have to do is download it and send it, via E-Trac Exchange, to your machine. Within minutes you can be hunting using it. And, like the SE, you can change it one the fly to suit your conditions.
There is also a coin pattern by theBeepGoesOn that he uses in Houston parks to coin hunt. If you happened to live in Houston, bingo he's done all your work for you. Connect, download and go hunt.
So, there are arguments for both machines. I originally purchased an SE, air tested with it, read more forums and books decided I should have gotten the E-Trac. So, I have a brand new boxed up SE and, I hunt with a E-Trac
Also, check out this
thread by Bryce-IL.