I like to have gravity helping me.
Bruce
From:
Three Rivers Forestry
"When obstacles prevent direct winching, or when the remaining trees are to be protected from damage, a self-releasing snatch block should be used. The Farmi snatch block releases the cable when the keyhole slider reaches it. The snatch block is attached to an anchor tree with a nylon strap which prevents damage to the tree. The automatic cable release works only when the pulley is turned upside down, which is when the release mechanism is facing the ground. "
Bruce