One site's take on the situation: http://www.marvistavet.com/html/body...ital-Or-Clinic
I think they come off a little negative about low-cost clinics, but they give some good information.
Bottom line is: it is better to have a cat spayed/neutered at a low cost clinic, than not at all. I would search around though....the "spay/neuter" clinic in my area (Ontario, where we don't seem to have any low-cost options!) is not much less expensive than my home vet (where they stayed overnight and received post-op pain killers).
Although I see the reservations of the "assembly line" method, I also figure if a vet is performing that many spay/neuter surgeries each day, he/she must get REALLY good at the procedure pretty quickly!