Here's something I posted over on the BM forum a few days ago. Not quite the comparison, but I'm guessing the Alias II is fairly close to the Alias I. Bottom line (for me) I'd say the order goes Um, then very close behind Sebenza then really far behind Alias, however I'm not all that price sensitive.
So I recently got an Umnumzaan and an Alias II. They are all fairly different feeling knives. I will say that carrying the Um around for a few days has given me a new appreciation of the Sebenza. I've also opened up the Sebenza and cleaned out the factory gunk and put in some Tuff Glide (didn't feel like dealing with all the heating, etc... for the Militec). It nows opens up somewhat faster, much easier to flick open, though I still won't be doing that much.
So here are some notes.
Blade Play: Sebenza/Um none at all, totally and 100% rock solid. Alias II came to me with quite a bit of wobble, I've adjusted the pivot (which has a tiny sweet spot) but it keeps loosening up, I've applied some blue loctite, so we'll see if that fixes it.
Opening: Sebenza is very smooth, can be flicked open with a bit of wrist action (this is after I added the Tuff Glide, before this it would take much more wrist action). Um also smooth (had to be worn in some, also replaced the factory gunk with Tuff Glide, but will probably spend some time next week and try some Militec) can be flicked open somewhat easier then a Sebenza but not as easy as some of the better Axis knives. Alias II the opening on this knife is kind of interesting, I find that I can only open it consistently by flicking it open. Pushing on the thumb studs slowly doesn't consistently open the knife for me, however flicking it open does. It flicks open lightning fast (much faster then the Um), almost looks/feels like an assisted opener.
Closing: Sebenza is probably the best one here, its got a nice cut out that allows for easy access to the frame lock. This is one of the Um's failings (IMO) I don't know why CR didn't create a similar cut out but I find that there's not much room for your thumb to get at the frame lock. The Alias II is better then the Um but not as good as the Sebenza.
Construction: Both the CRKs seem to be quite a bit nicer then the Alias (though a lot of this is subjective on my part). The Um seems to be a simpler design (fewer parts) then the Alias which in turn is simpler then the Sebenza (number of parts wise). The Um has very large perforated washers which are pretty cool. The Alias has two small washers (however this may be because its the smaller knife). The Sebenza has one large and one small washer.
General: I really like the feel of the Um, feels more ergonomic then the Sebenza. The swedge thing on top of the Um seems a bit silly (to me) but doesn't really bother me, though I'd probably prefer a more classic blade style. I like the glass breaker on the Um, though really I doubt I'll ever use it. You need a special tool to take down the Um, CRK doesn't include this or offer one for some reason.
Overall I think I like the Um the best, just feels the best in the hand and opens really nicely, if it just had that Sebenza style cut out it'd probably be close to the perfect frame lock.
Now if only BM would produce an all TI Axis lock with the fit and finish of the CRK I'd be in heaven.