This is the Bookeen Reader with a 5" screen. I don't know if we knew it was called Opus, but early pictures released by PocketBook were actually mockups of the Bookeen device (
Bookeen and PocketBook in possible legal dispute over 5" model). The "motion sensor" is probably to detect screen orientation and automatically switch the screen layout. The PocketBook device has this too. It allows one set of keys to work for left or right hands, although this would only apply to landscape mode with these keys.