ND filter quality necessary for video

I'll soon be filming a travel movie/documentary with my 5d Mark II, and I'll be using mostly lenses with a 77mm diameter, at least in daylight shoots.

If I want shallow DOF scenes in bright daylight (the location is Laos, which will most likely mean sunny days) I'll probably need some ND filters. However, I don't really use ND filters while taking stills, so I wouldn't want to buy real expensive ones if cheaper ones would be ok for video (since the video quality doesn't come close to still quality on the 5d).

Are there any reasons for buying more quality ND filters if I'm only going to use them only while shooting video?