I've owned both the small 21 (plain and Micarta) and small Inkosi (plain, very briefly!). The small 21 is just large enough for me to get a solid, comfortable grip. The blade is just long enough to fulfill all of my edc tasks and some food prep, especially in insingo variant. By contrast, and much to my surprise given the similarity, I kept the small inkosi for a day before deciding to return it. To me, despite being only marginally smaller, the small inkosi fell short in terms of grip and capability.
I have medium to large sized hands, and could not get a solid four finger grip on the handle, and the finger grooves caused hot spots. The blade, despite being only marginally shorter, felt noticeably less functional. Granted I only tried the clip point, perhaps the insingo version is more capable. Either way, the handle just didn't do it for me. The small 21 insingo really just is perfection to me, and the Inkosi, as close as it is, isn't.