It's rather slow if used on its own and is very frame disadvantageous on block whether it's cancelled into or not. The main use for this move is to cancel into it from K's close standing C as a combo starter.
This is also K's most reliable cross-up tool, but the spacing is still kind of tricky to get down. It also causes more hit-stun than jumping A so it's easier to combo off of. The animation is similar to that of jumping A, which is aimed pretty much straight down below K'.
Can be used as a deep hop in during hop pressure And when cancelled into Eins Trigger, his sweep becomes less vulnerable to being hopped over, and its recovery is shortened substantially.