Thanks for pointing that out. I hadn't read the whole thread.
Most of you probably aren't going to agree with me for what I'm about to say, and that's fine. For full disclosure I own a Sebenza 21, an Umnum, a Strider SnG and an SMF and a bunch of excellent fixed blades. I switch between carrying the Umnum and SnG as my edc.
There is no doubt about the function of the Umnum for basic cutting tasks. It is beyond excellent. The tanto blade I have on mine is a thing of beauty (and function) and is surprisingly easy to keep razor sharp by using a leather strop. The problem for me is, the Umnum, for all practical purposes, falls into the "harduse" category of knives. These are knives that people (military, law enforcement and SAR) depend on for saving lives. In all honesty, if I had such a life and death occupation, I would probably carry the SnG or the SmF as my first choice.
Every knife has weaknesses and will fail at some threshold of abuse, and I know the SnG has at least one documented weak spot, but for me the ceramic ball design of the Umnum is too much of a tradeoff in favor of "ease of use" and "mechanical bliss" at the expense of outright robustness. While I do not wrist flick my Umnum, I do thumb flick it all the time. It *is* mechanical nirvana. However, given Mr. Reeve's acknowledgement that an even slightly out of tolerance ball will cause the lock to fail, if my life depended on it, I would not opt to carry the Umnum.
I have some other nit-picks with the Umnum, such as how cumbersome it is to open with your left hand -- that would also tend to favor the SnG for use in a life or death occupation. Overall, the Umnum is a fantastic example of engineering and machining (true craftsmanship), but may in fact be over-engineered, at least for certain jobs/scenarios.