It's true this would be useless in heavy brush or blackberries. I mainly like it because it'll keep them from snacking on my fruit
trees. The amount of grass inside is perfect for one goat for one day to keep them from getting an upset rumen on the spring grass. I can swap out goats (I'm currently at 20 with all the littles) and move it repeatedly without overdoing it on anybody's digestion.
To get into heavier brush, I would use the electric netting. It's costly but if you take care of it, it'll last for years and years. It's also much cheaper and much more useful than trying to build permanent fencing as you can pull it up and move it easily. You will have to clear a path for it to run with a weed eater or something, but that's easier than clearing the whole thing. I
should add that goats will eat blackberries but they don't eat the mature canes. They will strip every bit of green off and eat the younger shoots but be prepared (if you get goats) to go in after and knock it all down. One plus is that if they continue to eat the green stuff, the canes will eventually die!