I have a Dainese 'Nero'
I have only used it once so not sure whether I'm qualified to speak yet, but I found I was a bit stiff, but It was extremely cold weather and had snow on the side of the road, also it may have been something to do with my jacket being a bit tight with the back protector in place and the back padding in the jacket, may be next time I remnove the jacket padding when I have the protector in place.
One thing that did annoy me was the protector would push the back of my jocks down when i sat upright and when ever I got off the bike I was pulling them back up again.