I have both, and prefer the Sebenza for EDC over the Umnumzaan.
No doubt that the Umnum slices well, but in order for it to have the same geometric triangle ratio as the Sebenza's blade, the grind would need to be 3.28 mm taller IIRC. The tip of the Umnumzaan is ground differently than the Sebenza, and I'd trust it to pry with much more than the Sebenza's blade.
I prefer the ergonomics of the Sebenza, as the clip on the Umnum can sometimes cause hotspots in the hand after 10+ minutes of use. I have yet to get any hotspots from the Sebenza.
I'm of the opinion that aesthetically the Umnumzaan is something that you might see in a froo froo interior decorator's pocket (there is a Japanese word that I'm forgetting, which doesn't translate well to English, that is apropos for what I am trying to describe). I think the smoother lines and more balanced look of the Sebenza is more appealing.