I use Weber's three sided brush and feel like it does a good job. I brush my grates during the cook if they start to get gunked up, and at the end of the cook while everything's still hot. I've read a number of articles that talk about these bristles being eaten, or found in food, but they never describe the type of brush they come from. I'm guessing they're more likely to come from the style of brush that's a lot like a toothbrush, in that it is comprised of groupings of bristles shoved inside little holes and somehow held in place by friction, or melting the plastic around it. (I hope there's more than friction used for the wooden designs) The Weber three sided brush (among others) twists longer lengths of the scrubby bristles around and in between thicker wires that solidly (to me) hold everything in place. I feel pretty confident in that design/style.
However, metal fatigue is a consideration if an individual bristle gets folded back and forth in the same spot with a scrubbing motion. I'll periodically inspect and flex the bristles on my brush and so far, haven't found any to be suspect. Annual replacement is probably a prudent idea.
That being said, does anyone have much experience with any of the steam scrubby pad-type ones?