Perception of brightness is logarithmic, so 10x more lumens would make an image appear about 2x as bright. You can check out a video here:
M109S Review on Gearlog
In real-world terms, you can expect to get about a 15" image in a brightly lit room with sunlight and about a 40" image in a dimly lit office with no natural lighting.
I'm actually pretty tempted to get one except for two issues. The first is an annoyance and the 2nd is a deal-breaker:
1) No remote and the touch-sensitive control pad has no tactile feedback.
2) No zoom. Image size is entirely a function of how far you are from the projection surface.
I'm not entirely sure, but I imagine that this projector has no perspective correction so if you're not square with the "screen," your image will be distorted. Again, not sure on that one. I'd research to find out if #2 wasn't already a deal-breaker for me. :brokenheart: