Same idea as the Firehawk, getting better blacks from chip projectors (LCD, LCOS etc) if I remember the Firehawk correctly but with less gain. Something on the order of 0.9 vs 1.3 for the Firehawk. I believe it was Stewart's first gray screen. Did wonders for the Sony 10HT I had at the time. At the size I'm using it's certainly bright enough and has about a 2x wider viewing angle to half brightness than the Firehawk.
Can't say it would work as well in much larger sizes without a really bright PJ and room lighting has a bigger impact than the higher gain screens.