Why do you think it would be hard to manage the lock on the small? What size knife do you carry now? Also what are the knife laws in your area for what you can carry?
Those are all things you should think about. I find my Small 21 and Small Inkosi to be easy to operate. The Inkosi is the easier of the two even though its slightly smaller. The small sebenza fits more hand sizes then the Inkosi, but even people with large hands can like the small Inkosi. Its really a try and see if it fits you on that model.
One thing I have noticed is the large Sebenza is a little smoother operating then the small Sebenza. I think the longer lock bar is part of that difference. Over time there is not much difference but fresh from the box its there. The Inkosi is easier and smother then them both.
The best thing it to go to CRK and check the dealer list and go to a store where you can handle them both. No one else can tell you if your hands will have an issue. Other then that I suggest buying a used on on the Exchange. If you don't like it you should be able to sell it back for what you paid for it here. Or buy from a dealer that will allow you to return the knife if it does not work for your hands. Selling a CRK bought new is going to lose you $50-$100 depending on model and the demand at the time. Which is why buying on the secondary market works out. Most of the time knives on the exchange here are never actually used just pre-owned by collectors.
If you have the money you can always buy both sizes on the exchange and sell the one you don't like as much.