SOOO useful in different ways.
Last use was to tip tie 40' leaders off a smaller rigging point with the BMS BS, while butt tying a second line to carry most of the load. This means I could remotely tighten the tip-tie, then lower, without a doubling of force had I used a block. Once the piece was free, one groundie passed me the standing end which I controlled, while they lowered into a very narrow DZ.
We routinely run two man crews. I cut and lower a lot with NC rigging or the BMS BS. The groundie can catch a limb or top or log, then pass the standing end to me in order that I can lower it while he lands it.
The is a thread about it here that I started (search by user name), as well as one on TB titled O.L.D.S. Tom Dunlap is a big advocate, and to my knowledge the one that started using it in trees.
SOOOO worth $110. Doesn't replace porty and the like, but a great tool.