I haven't had any comments at all about the "box vs. knife" issue (nor the "plastic vs. paper" issue). OK, had to toss that last part in there.
There is certainly less fabric in the box pleated than in the knife pleated - which is both a positive and a negative. Less expensive? Box pleated. Less weight to wear around? Box pleated. Perceived as more "traditional" (though Matt will undoubtedly weigh in on that)? Knife pleated. More "swish, sway, and play" of the pleats? Knife pleated. A "cleaner" (less "busy") look from the rear? Box pleated.
Tis a struggle to figure it out!
So it all depends on what you're hoping for out of this kilt... hope this ramble helps a bit.
No matter what you decide to sew, enjoy it and wear it well!
(Oh, and thanks for not asking the "sett" or "stripe" question.)