I bought a set from Asia and, though they don't have the range that these do, I found that they helped quite a bit. Front end feels more planted over bumps and road irregularities and they don't dive so much on hard braking anymore.
Put them on today. That was really a nice surprise. I know increasing preload is kind of a stone-axe way to stiffen a spring's feel, using up a bit of its travel and compliance, jacking it up a little overall. In this case it's 13mm at minimum preload and that's how I did the first ride.
By golly, the dive on braking is lessened and it's not quite as pillowy feeling. If I were racing or some balls-out canyon carver I'm sure I'd want to delve further into fancy fork fixins, but this falls nicely into the "Wish they'd just done this at the factory" category. Much more effect than I'd expected.