I have been using my Piranha for both brush clearing and getting under some rocky soil. I found the PB was great for getting through two sections with 6-9 inch rocks embedded where my bucket would just hit and I would have to dig under each rock. So the bar saved me an hour or two of work.
For the brush, I was able to take out a 20x20 foot section coming from 2 sides in about 20 minutes. Only thing is I have some real rubbery vines that break about a foot from the soil, need to figure out how to get the bar under these without moving too much soil (on a slope).