I currently have 14 CRKs so obviously I feel they are worth it. However, I like many of my Benchmades, Spydercos, and Zero Tolearances just as much. If you're strictly looking for a great user you can get one from one of those companies (or others) that will perform just as well for half or less of what a Sebenza will cost you. But if you want to experience a CRK, there's only one way to do it... I do recommend reserving final judgement until you've owned it and used it for a while, a least a month. I was really unimpressed with my first one but I picked up a few other variations trying to find the allure. The more time I spent with them the more I appreciated them. Now I can't imagine my collection without them. Most of mine are just for collecting but I do carry and use about five of them.
Are you set on a 21? My favorite user is my plain 25. It gets carried a lot. The ergonomics work get for me and I love the ceramic ball locking interface. It doesn't have the coveted pivot bushing but its action is actually smoother than most of my 21s with no blade play and the pivot never comes loose. The 25 was replaced by the Inkosi which is available in large and small.
I've done a few CRK videos. You might find some useful info in them:
https://www.youtube.com/user/photoman12001
A few of these are gone and a few new ones came in.
You'll notice that I replace the pocket clip on all my CRKs with the insert. I much prefer the feel of CRKs without the clip.
I carry them in my EDC bag or a leather slip sheath in a pocket.
Love the 25s
I slightly prefer Classics to 21s but the differences are mostly cosmetic.
I'm a little "meh" on the Regulars but they are great collectables.
Sebenza evolution botton to top: Regular, Classic, 21, 25
The Insingo blade is a great option too.
There was a point to all of that. If you end up liking your CRK, be prepared to buy more.