After much research, I took a shot, and used it to start up a 46g tropical community tank.
Set up the tank with conditioned water, waited a day, then added Bio-Spira and what was probably, oh, a "2/3 maximum" fish load. My tank cycled (to 0 ammonia, 0 nitrites, ~10 nitrates) in nine days. The highest ammonia reading I got during that time (with daily testing) was less than 1.5 ppm. The highest nitrite reading I got was less than 1.0 ppm.
A few things I feel I should add:
1) The water conditioner I used was Marineland's Bio-Safe. Marineland is the company that makes Bio-Spira, and recently I've heard a few whiffs of rumors that Bio-Spira works better (or only works, according to a few people) if you use Marineland's conditioners (Bio-Safe or Bio-Coat). Like I said, just an inkling of a rumor, so I'd take that with a great big grain of salt.
2) I did see a minor nitrite spike (up to 0.5 ppm) about four or five weeks into the cycle. Two water changes, two days apart, and the nitrites went back down to zero, and have stayed there ever since (about seven months).
Whether this is due to the Bio-Spira is uncertain, because I was also experimenting with my filter cartridge cleaning routine during that time.
This is just a tale of what I experienced, one time. As always, your mileage may vary.