I recently bought one of these frames thru the ES buy/sell page. KHS doesn't make them anymore. When I was researching it pre-purchase, the online mountain bike crowd seemed to think that it was only a KHS thing, kind of a curiosity, but many loved the design for its relative stiffness compared to a FS bike and its versatility given the single speed design.
I've just finished building up the components but haven't got it running yet. I do have a FS build, and am finding it squishier and heavier than I need it to be. I also ride my partner's rigid fork e-bike a lot and it's too bumpy. I was thinking the softtail with a decent travel downhill fork (Manitou Nixon) and a rear dd hub motor would be a great middle-ground. I don't know if anyone else has tried these frames, but I'd be curious to find out. I'm hoping to have mine going in a few weeks. If the thread's still alive, I will post.