Nice Pictures! I have a few of these daggers myself, but I can't post the pics because I am traveling at the moment. I have also one example with the same double notches as the pic posted above.
Here is a link to a youtube video I found depicting 'ceremonial' use of a variation of these sorts of daggers. It is attributed to the Nara people of Eritrea who look alot like Beja to me. A fascinating video, with spears, shields, swords, and daggers and interaction between males and females. The dagger is shown between 3:00 and 4:00... Please post your observations and opinions on this video and these really cool daggers.