BIllhooks are fantastic tools, though you need the right shape for what you are doing. They come with a variety of hook profiles, the straighter ones being more useful outside of hedgelaying circles but they also come in double edged forms (straight on back of a hooked blade). The doubles are blooming dangerous IMO, but I use a couple of billhooks for all sorts these days.
Down in Devon a lot of old boys use them instead of axes for everything! I just use it instead of a machete/kukri/slasher typ big knife, also instead of a small axe sometimes.
the hook i use is fairly straight with a slight downward hook (one of my own making, of course
). It's about a 10" blade and I've been using it for scrub clearance, coppicing, shelter building, rope cuttin/tarp errecting, oh and I even put it into a cutting comp at a Belgium knife show in november
I've not got around to a sheath for mine yet (mostly coz I was supposed to be selling it, but needed a billhook at short notice myself
) so it just gets a bit of split hose held on with rubber bands to keep the edge away from things in my bag.