ALLATPS Lakeland, FL
I did it just over a month ago at ATP's newest FL location at LAL. I bought the Gleim ATP book, and even had access to Gleim's ATP CD-ROM, but darned if I didn't make any time to go though them, except for a few times in the "library."
I went into the prep session "cold." Like I said, I hadn't cracked the Gleim hardly at all. About 14 hours in front of the prep computer was about all I could stand, and I was able to make a bit of a gouge for the cross-countries and weight and balance sections. I figure I'll get all that in groundschool anyway. ALLATP has somewhere around 582 Part 121 questions out of the massive bank in the ATP book. Narrowing it down like that was worth it.
Drove home to Orlando that night and back to Lakeland the next morning to take the test. I finished in good time and got a 93 out of it. I had CFI friends at CAA that studied the Gleim and took it at the Academy and got in the 80s, but I seem to recall going over much of what was in the test bank over my flight-instructing career and don't think I short-changed myself by "cramming." 99% of the Comair CFIs do the ALLATPs thing and the hiring board at Comair doesn't seem to give it a second glance.
Bring snacks and take a good break for lunch and you'll do fine!
John, Longwood, FL