I saw it at the booth at CEDIA last year. It wasn't overly bright, but it wasn't 'dim' either. Kind of 'average' indirect light. The display they had allowed you to go up and physically touch the screen. That was the coolest part, was actually getting a bit hands on with things and really examining everything. It is what got me excited about it. Putting your hand up, seeing things appear normal, etc., then putting their screen up in front of the video and watching it really jump to life.
They had the split comparison screen which did a great job, and that one was mobile so I could put it in front of the projected image, move it around, etc. and see that there wasn't something really wacky going on.
The Flex screen also is (somehow) designed in a way that allows for a much higher viewing angle than the fixed hard screen delivers. I asked them about this and they said that they thought the demand for the flex screen would be greater in the home marketplace so they slightly reduced grain, but had a huge boost in viewing angle.
It was incredibly visible how much smoother the viewing angle was on the flex screen - but both images looked incredible considering the ambient light in the room.
Worth the money?
If I couldn't do rear projection from a light controlled room (garage/basement?) then I would seriously consider it if money allowed.