I have the utopia...Good product and have ridden a good 20000klm with it.
It reduces fatigue,not just for your back ,but also for your right arm, particularly in conjunction with a throttlemeister http://throttlemeister.com/ (throttle lock) so you can take your arm off the bars and lean back into the backrest.My only concern is if you get hit from behind, which may give you a spinal injury,though i searched a bit on the net and couldnt find any references.Sissy bars are known for spinal injury too, but hey ,its a calculated risk.
Utopia has excellent after sales service too...10/10 rubber chickens