I've had one of these blackbusters for a while (more than a year). Got it for $50 during a similar promotion.
It's worked very well. It's survived 3 power outages. I never left the computer on for more than a few minutes during an outage, so I don't know how long it would last, but it lasted long enough for me to comfortably shutdown everything
(plugged into it: 19" monitor, 533-850cranked celeron w 260w power supply, 2 harddrives, 2 cd, 5 pci cards incl. 2 vid cards, 2 sound cards, 1 ata100 card, also a USB hub).
This may be a + or a -, but my (lowend) APS used to trigger alarms so often (for power fluctuations) that I switched the fluctuation alarm off. This one only triggers an alarm if it goes into full battery backup mode.