I run my brakes pretty far inward to be much of a problem. I do punch trees on occasion but a flimsy plastic gard only supported on the inside isn't going to help much there.*cries in wait-a-while*
Lantana (a weed here) is more common, and just as gnarly but wait-a-while will nearly deglove a hand if you're not careful. I've got decent scars from getting little vines or tendrils snagged and then pulled through my fingers before I could stop.
I still haven't gotten brushguards or anything yet, but when I switched from Hopes to Dominions I noticed the brakes engaging the first few times I went too inside and dragged a bar end through a fern or bush.