For just over $400 shipped it's definitely worth a shot. It's a matte white screen material so my guess is that it will absorb a significant amount of light. They claim it has a velvet wrap, so hopefully that wrap rejects light and isn't the cheaper, more reflective velvet.
I'm not familar with the installation method they show. Hopefully it will provide a nice tight fit for the screen.
That's super cheap for a 100-inch wrapped screen.
Love the informercial video. That guy's voice is so stereotypical of that genre it's funny!