I'd keep them if it's your only one though. The S/D the blades give can make a difference in some situations if you care about speed at all, or don't have ready access to someone to cast higher levels of it. They are among the strongest daggers, though there are certainly stronger or more effective weapons, so it is mostly used for its special before switching to a more appropriate weapon.
Bought one for 2 PDs earlier this week, and have seen others sell around 2-3. But you have a HUmar and should definitely keep them (unless this is your second) because level 3 shifta is still much better than no shifta (solo mode or playing without someone who can cast higher S/D).