This kaskara seems indeed of high quality, and characteristic of those found in Darfur (western Sudan) rather than examples used by the Beja (pronounced bay'za) and Hadendoa of the SE Sudan. These tribes also are found well into Eritrea and parts of Ethiopia. In conversations a number of years ago with a man from Darfur, I was told these kaskaras were still held as heirlooms and worn on occasion by tribal elders. It would be extremely difficult to acquire one of these authentic older examples, however, like anything they do come up occasionally. I spoke also quite a few times with a man from Eritrea who was Beja, and he actually had a video of tribal dancing using some of thier edged weapons, including kaskaras. After watching this at full volume for some time, I started to really get into the tribal chants and rhythm, which finally drew my wife into my den to see if I had lost my mind!!
Brian, without checking further into to archival web here I am pretty sure the knights helm was Kirshbaum of Solingen, indeed mid 19th century, and a very prolific supplier of blades to the British ( I have a M1853 with Kirshbaum blade). During the Mahdist period, Darfur was reluctant to participate in the rebellion with the Mahdi, and I believe were somewhat inclined to intrigue with British forces, if that might be a denominator in explaining a German blade via British intermediaries.
In any case, it seems doubtful this would be a Mahdist relic in my opinion, but still an outstanding example of kaskara from Darfur regions.....though with typical trade and diffusion....who knows...maybe a Beja did acquire this weapon...but only distinctly supported provenance could say.
I will once again mention what I have noted in discussions on kaskaras for over seven years now, none of these tribesmen I have spoken with, nor any other Sudanese sources with whom I have consulted, have ever heard of the term 'kaskara'. To them it is simply termed sa'if.
All the best,
Jim