Thanks for the information.
One thing to keep in mind is that ATP normally considers for flight instructor positions only those students who have completed the ACPP program with them. Due to the high instructor turnover as a result of strong regional airline hiring, they are now also consider anyone who completes their CFI programs. However, as I have said before, we really can't rely on the current regional airline hiring continuing forever, and there is a chance that if you don't do the ACPP program, you may not be able to instruct with them. (Not sure if that's a factor for you or not, but I think it's something to consider).
In my paranoid mind, I'm thinking that if in fact getting a job at a regional does become more competitive, having the ME time that you get as an instructor at ATP could make a big difference.