Fader ND Filter question

Looking for a ND filter for my Panasonic 14-140 lens, so I can keep my shutter speed at 1/50 for 24p and still be able to use larger apertures for DOF control, and I've discovered variable density filters. Looking specifically at the Fader ND filters, I see they have a Mk II filter, and a HD filter which they say is optimized for HD video. Can anyone tell me if there is enough difference between the two to justify the $80 increase in price for the HD version?

Also, if I'm planning on starting out with just one ND filter, since these variable units aren't cheap, would I really be gaining anything using one on the 14-140 zoom, at least for video, since I'm not really going to get a huge amount of DOF control with it anyway? Maybe I should look at getting one for my 20mm 1.7 instead?