A friend at uni had a standard wrap-around bull bar on her 90. She drove into something at low speed, the bullbar folded back on the bumper and trashed both wings, slam panel and bonnet as well as small things like lights and headlight surrounds.
Without the bull bar, the bumper would have bent but that would have been the extent of the damage, which can be fixed in 5 minutes with a sledge hammer.
IMO they do offer protection from animals, small branches and wheelchair users

but aren't great on more solid objects unless attached to a more sturdy bumper.