Like everyone else's super shotgun. It does NOT reduce turning speed. Further nails have a culmative efect, but the law of diminishing returns kicks in. Instead of the crowbar, a close up only weapon - but deadly. Used correctly it can gib a healthy HWG in one swing.
Correct use is to hit the back of the head.
To the from it does very little damage, though repeate swings will still kill stuff. This weapon from the back ignores armour it seems. Grenades, normal, up to 4. VERY useful to the spy, since their use doesn't remove the disguise. Right - now onto the mechanics of their class specific abilities.