A Sebenza is a Sebenza and is a unique and first-class product. If you want one bad enough, you'll eventually save up and get one. As to this deal however - the Alias II is a very nice knife and (from the pictures you've shown) this seems to be a good deal. I would imagine that your satisfaction level will be high, unless not having the SEB keeps you up at night. I would buy the Alias until such time as you can comfortably afford a Sebenza. Just make sure the person you are dealing with is reputable and you'll been fine.
I will predict that if you buy the Alias now and a Sebenza later, you'll probably end up carrying the Seb 90% of the time. That seems to be the pattern. (HELLO MIRROR!)
As far the the Alias being backordered, I have some info I can share. I had the same question about the seeming lack of availability, so I emailed Bradley Cutlery and got the following response:
"The Alias and Alias II are currently unavailable until an agreement with a new manufacturer is established. The Underboss is available at this time on our website. Please visit us regularly for updates. We appreciate your interest and apologize for any inconvenience."
So - I imagine that the Bradley/Benchmade agreement has expired and the Alias family is done for now. FYI.