...and wouldn't want to go back to working without one. Makes it almost too easy to set and douse the chute.
A buddy of mine bought a fairly cheap
generic sock commercially available, and melted the blocks. As in all sailing, beware of cheap
fittings. My sock was made by the same loft that made my spinnaker
(North Sails) and is of considerably higher quality. Also has a nice carbon-fiber snuffer, which is important when you consider weight aloft.
So, yeah, they're great, but don't forget that you get what you pay for.