This is my understanding as well, but I'll add that these three options are considered full admission to TAMU.
Blinn Engineering gives you full privileges - you can live on campus, be in the Corps, rush a fraternity or sorority, have a dining plan, etc. You just have to take your first two math and science classes at Blinn, which are taught by TAMU professors, and all of your other classes are on main campus. Once you complete those 4 courses at Blinn you go through ETAM like everyone else and get your specific engineering major.
At least this is what I understand ... hope it's all accurate!