As someone who took the ASA Fasttrack route, I feel it was worth it. When I was at FSI, I took heat for the fact that many felt I was "paying" for my job. I don't want to come across as negative on flight instructing, but it seems like that too is "paying" for the same job, just in a different way. Instead of out of pocket or loan expense, you pay with time. Time spent at a low pay rate as a flight instructor. Time spent without an airline seniority number. And by the time you pay for ratings to be a flight instructor, it's not that much cheaper than the ASA program (at least at FSI. You could go to a part 61 FBO and save a ton of cash getting your ratings.)
As far as the ASA program goes, don't let anyone convince you into thinking it's going to be easy. It's a whole new world of stress. They'll give you a little leewway in the beginning, but you need to be up to airline standards of flying in 30 hours. They aren't kidding about that. And the Saab doesn't get any easier. However, if you make it through, and most people do eventually, it is great prep for the ASA training.
Keep in mind, flight instructors do NOT get the entire ASA fast track program for free after their 800 hours. They get 8 hours of training in the SAAB. Some might get lucky enough to instruct in the seneca/ASA program, but certainly not all of them. Several of the FSI flight instructors have had difficulty in training at ASA (and other airlines.) Sitting in the right seat teaching steep turns all day doesn't help all that much with keeping current for an airline job. I'll agree that instructing definitely helps you to learn a lot about flying airplanes, as there's no way to learn something like teaching it. The point is you really need instrument experience (both with mental situational awareness and flying) and practice with the two person crew concept, which is not traditionally stressed in training for ratings.
Hopefully I've added something for people to think about. The real point is getting to the majors as quickly as possible. Each year delay in getting there costs about $500,000 over a lifetime of earnings, or so I've been told. Don't hold me to proving that statistic.
One other thing. Right now, it takes 2000-3000 hours and at least part 135 experience to get on with ASA if you come off the street. While other airlines aren't quite so high, it'll still take more than 1200 hours to get on with an airline.