The first seems like it can get confused with genjutsu when it's actually just the user giving off killing intention. This technique requires for the user to be focused on the target, which also means the target must be able to be seen by the user. So if the target gets out of the line of the user then they can possibly avoid it. The jutsu can be used on multiple target's, but it begins to lose it effectiveness due to the dividing your consciousness and focus on more than one thing. The less the targets there the more effective the technique has a chance of being. Killing intent also deals with range, as that plays a big role in how effective the technique will be. When using this technique the user's rank and target's rank are important factors to consider since that determines the intensity of the jutsu. The way this jutsu can be dispersed is also similar to genjutsu, since the target can get rid of it through pain. Or a killing intent of their own. The fact that this jutsu requires complete focus on the target, and that the user can't mold chakra during this process can be seen as drawbacks to the technique.
For the next one, it's a good technique to use to strike an opponent from their blind spot. Once learning the right techniques to combine with this jutsu like you said, it can be a really deadly jutsu. Also, it appears that this technique can only be used in short range which can be a drawback.