This question all depends on your intended use... Overall, the Mini Manix will probably cut/perform better than the Large Sebenza. I have both a regular Manix and a Large Sebenza, and there are definite differences, some of which I think make the Sebenza a better knife.
The Sebenza's fit and finish are definitely superior in most ways to the Manix. It opens more smoothly, especially after using it for a while, and it locks up perfectly every time. Another great thing about the Sebenza is the fact that you can disassemble it with relative ease. This is great for times when you want to clean the dust out and relubricate the pivot. The Sebenza also will not depreciate in value like the Manix will, especially if before selling it, you return it to the factory to get it refurbished.
The Manix stands out on a raw cutting performance basis. The full flat ground blade cuts exceptionally well, and resharpens easier in my opinion due to the more acute edge angle as well as the fact that the edge has not been slightly convexed as I found my Sebenza was. The Manix, at least the regular size one, is an ergonomic dream. I feel that you will be able to retain the Manix better in your hand both due to the ergonomics and the grippy G10.
You posted concerns about pocket thickness. You will get used to either knife in your pocket after time. The thickness has little to do with that, and I have found the Manix to be just fine in terms of thickness. One thing about pocket carry that I have noticed, though, is the Sebenza has the tendency to slip out of pockets made of thin material. I usually wear jeans, so this is irrelevant, but if you are wearing clothes made of very thin material on a regular basis, the Sebenza may have problems with this. On the other hand, the Manix, due to the G10 handles, can tear up pockets pretty quickly. A solution to this is to sand down the clip side of the handle so that it is less abrasive when removing the knife from the pocket.
Well... some conclusions now...
If you want a classy knife and work in a place where you get to/have to dress relatively well, I would suggest the Sebenza. If you work in a place that demands a lot out of your knife, to the point of cutting some pretty tough things, I would go with the Manix, both due to the fact that you retain it better in the hand, and the fact that it will cut more efficiently. If you're planning on reselling the knife, the Sebenza will get you more.
To put things simply, the Sebenza will cost more, and it is definitely more refined. If you need a cutting tool, however, get the Manix.
Neither knife will let you down. It comes down to taste.
Travis