So the BK-40 is already in my hands. Thanks, Tomars!
Thoughts:
For the price point, they've done a good job.
It is TOTALLY a Tweener Folder. Just is exactly that.
The blade shape is *gorgeous*. Looks well-ground and finished appropriately. Very nice to the touch. All the dimensions are well-balanced.
Action is smooth, but not fast - fine. That will slick up with use. Lock-up is positive. I THINK the lockbar provides both fore and aft stability when open. I don't think there's another stop pin? (looking from the outside) When closed, it appears the detent and the back spacer are the stops.
I don't love the feel of the handles and they have some flex to them. Makes me want to retrofit the blade and a lock mechanism between a set of tweener micarta!

(no no, that's probably not a thing)
I'm not sure how I feel about the tweener handles on a folder. LOVE them on a fixie.
For making something that is unquestionably a Becker Folder with good ergonomics, it's spot on.
I might want smaller, tho.
$40 for a set of handles on a custom blade is cheap. That's the cost of '62 or Tweener micarta scales.
If the spine had more features, perhaps the thumb studs could be designed out.
Compared to an 'actual' tweener (or actual tweener dimensions, anyway), it's spot-on:
I'm just thinking out loud here...