The ZT 0640 is indeed a fine-looking knife. It's actually a very old Emerson design. Despite more modern attempts to include it under the tactical period genre
it really goes back to Emerson's art knife days.
It was one of the designs that he used to cross over, incorporating it into his early Viper lineup.
I think the original question has been answered pretty well in this and other threads. But I'll add my two cents. I bought these Emerson Knives, Inc., models back when they were representative of the state-of-the-art in folding knives.
They impressed me when I got them, I continue to admire them, I wouldn't hesitate to carry them (and occasionally still do), and I would be very reluctant to part with them (we've shared some miles). They definitely spurred me to purchase other EKI knives.
In the roughly twenty years that have elapsed since I bought them, however, they no longer reflect the state-of-the-art in folding knives. But their construction (materials and techniques) still represent EKI knives, and I think that's been a blind spot for Ernest Emerson. It's one thing to stay true to your roots, but it's entirely another to ignore industry advancements in, say, materials, fabrication methods, lock technologies, steel treatments, etc.
You can't rest on your laurels and remain relevant. I believe that a lot of other companies have surpassed EKI in the tactical knife realm because they've been more creative and forward-leaning in adapting to changing times. The sad thing is, a number of them have done so by advancing Emerson's own ideas.
-Steve