It's certainly not a high quality product that you get back from the rasterbator site. Nothing even approaching photo quality - more like what you would see in a black and white photo in a newspaper, only much larger. I've made images that measured about 5 by 7 feet, and were easily recognizable from about 40 feet away. People's faces could be identified, as well as major features of the original image, but not any fine details.
Be aware that printing these files takes huge amounts of ink/toner. You're basically printing 25 or more pages that probably average 50% coverage or so. I usually did them at work on a laser printer, and had to print in 7 or 8 page chunks so the printer didn't overheat and leave streaks.