1.) I have had the tanto umnumzaan. I found it to be an amazing slicer, but that was about it. The tanto looks cool and all but is and will never be as functional as a regular pointed blade. Out of the 3 umnumzaans that I have owned ( stat-tac, tanto, regular ), the regular version is hands down the best. The star tac looks nice, but its grooves are sharp and makes it uncomfortable to hold tightly when in use. After stating that awhile back, I got several PM's from others stating as much, but did sold them rather than state as so. I sold mine because of this only. The tanto felt great in hand just like the original, but the blade shape as I stated is limited. I would say to let that one go.
2.) I dont have any experience with the insingo. I do want to get one eventually and I just missed out on one recently. I would go for the large myself as thats what I prefer.
3.) The large regular is by far my most favorite sebenza design to date. ( I really love the large P sebenza, but they are too rare to go and on about ). The large regular has everything I love about CRK. Fit and Finnish is perfect CRK Craftsmanship. The regulars handles are rounded and fit your hand perfectly. The blade shape is absolutely perfect. I HATE the super pointy 21 blade shape. The large regular just has it all and thats I carry daily. Lately its been a large regular In God We Trust. I got it used and scuffed, so I can use it away.
Out of the 3 you mentioned, it would be hands down the large regular sebenza.