I am not 100% sure I understand what wideband mean in this context.
According to the Kenko brochures
(
http://www.kenko-tokina.co.jp/e/P.12_13.PDF ) Japlish explanation:
"WIDE BAND makes Digital SLR camera's viewfinder image color
difference has been corrected"
As far as I can tell, the Kenko (which I have) is identical to the
Hoya. The features list is identical, namely:
Digital Multi Coating, Black Almite
frame, Black Rimmed Glass, Low Profile Frame, Knurled
Frame Edge, UV protected Cases
For my filter, the par that rotates is about 3mm thick, and the
knurled section on the threaded part ads another 2mm. SO it sticks
out about 5mm in total, which is the same as the hoya. I'd say the
Kenko is about 1.5-2 mm thinner than my stardard thickness Hoya
Polarisers.
The Kenko looks physicall identical to the pictures that I have seen
of a Hoya Pro1 D Cir-Pl. Even the fonts used in the writing is the
same. Just the Kenko has Kenko instead of Hoya written on it.