I was a student at ATP as well as an Instructor with them afterwards. I went through the ATP MSU degree program before that fell apart. it was similar to the self paced program. Took me about a year and a half to go from zero to hero(no flight time to CFI). The length was due to the eight week semesters per MSU. My experience as a student(I went the the PHX location) was excellent. I had really good instructors, and even the other instructors around we're pretty knowledgable and helpful when I needed any help.
You have to know the way ATP operates is their programs are based off the minimum amount of flight time to be able to qualify for the practical. So Aviation and studying is your life, I cannot emphasize that enough. I didn't go through the 90 day program but most of the other students at the school were, and I also instructed my own students through the 90 day. So I understand first hand the stress involved.
I like to think I was lucky with my training location and the instructors. You have to know ATP guarantees the job to everyone who goes throug the program *AS LONG AS YOu DONT HAVE TOO MANY BUSTED CHECK RIDES*. Because of this you will have exceptional pilots, but being a good instructor is another thing. There were instructors that I knew and worked with that were only there because it was a job. They did not like instructing nor did they want to be there but they didn't have another options. The result of that type of attitude is bd instruction. If this is the case,however, simply ask for a new instructor and you will most likely be given one. It's an easy fix.
Overall my experience with ATP was excellent. They provided me with the opertunity and great aircraft to get where I am today. Plus their connections with regionals is still helping me today. I would highly recommend them as a flight school.