Yep, ID numbers. Basically they would represent a quarter. Since I got my first two silver quarters (washington and slq) recently the numbers are engraved in the back of my eyelids.
The E-Trac is much better than the SE Pro in my book... but that's just me, and my money. I actually paid full price for both. Now when you make the comparison, you are probably comparing a used SE Pro to a new or used E-Trac. That gets a little trickier because the SE Pro is a great machine, and you are getting a lot of value for your dollar. You just get some extra nice features for that wad of cash more for the E-Trac. I think you'd do just fine with the SE Pro, but if you can afford it get the E-Trac. If you can, try both for 10 minutes of detecting. Also try twiddling the menus for 5 minutes.