I have never worn one, they look very uncomfortable but I suppose
they do stop you from hurting your back Undecided.............

I wear mine all the time. Its like a helmet you get so use to it you don't even realize its on. They do make more than one kind I prefer[well only use] the block kind. They are made up of multiple small blocks that are only 2-3" wide, they really conform to you. They also make panel vests it has one back piece and a left/right in front. I personally don't like the way they fit, but my daughter wears hers every ride. Not only do they protect your back, but all internal organs and collar bones as well. Took a pretty serious fall and tore the tendons off both sides of my ankle-The only thing NOT protected-helmet and vest on.