Cancelling back-dashes with up/down to cover more distance in less time. Back, back, down, back, back, down, back, back down... I'd assume it's called Korean Back-dash because it was discovered by a Korean player, but *shrug*
I suck at Tekken and have only been playing it a couple weeks, so take the rest with a grain of salt, but I like to try and understand the mechanics of fighting games.
first, you ARE blocking during the backdash as long as you HOLD your back command. You are vulnerable to mids during the time that you're crouching (obviously).
for the backdash to work, you start off with b, b, then d/b, N, b, db, N, b, etc. When you let go of d/b, you need to have a a b command register as well to count as the first b input of a backdash (turn on command history), and the neutral is between releasing the d/b and pressing b again, which would count as the second b input of your backdash.
The reason for the neutral is because you need a b, b command to backdash, which is actually b, N, b. If you don't hit neutral between the d/b and pressing back again, you won't actually go back into a dash.
You can test if you're doing it correctly by just holding d/b for as long as you want, releasing and then pressing and holding back. If you do that part right, you'll get a backdash.