haha

its a limited slip differential, meaning when u pop the clutch to start a race. u will leave 2 solid rubber marks on the ground, as opposed to one big mark with a stock open diff.
in simple terms: its a part of the tranny that forces a "even" distribution between the two axles. a stock open diff tranny biases more power to one side, and generally once u lose traction on one side it will run away with it, because the diff will bias all the way to the loose wheel.

the LSD should come factory installed in those trannys, i believe its just a factory LSD equipped tranny, your not buying the LSD separately with those deals. i actually have a b16a LSD equipped motor showing up tuesday for my friends civic. its a good deal. considering a QUAIFE LSD is around $895 for the part only, not counting labor to install it.

getting a tranny equipped with LSD for $300 is WELL worth it.

~boom