I never found I needed ND filters of stills photography (I've had a few in my bag for years and never taken them out of their cases to actually use). That's not to say they couldn’t have been used for some shots, just that I've never really needed them for mine. However, when starting to get into video, I'd read that ND filters are a necessity when recording outdoors (especially in daylight)! There are some cheap ones available, as well as some very expensive ones - both fixed and variable density. I toyed with getting a set of fixed ones but thought I'd test the need with an ND, and one in the middle of the price range. I also opted of the magnetic mount as it seemed a useful alternative to having to screw it on.
I've found that ND filters really are needed for video (especially with a camera that works best set at "ISO400") and this one has done the job for me. Variable NDs can suffer from an X pattern at their densest setting - I've not needed to use this one at its darkest but it doesn't appear to suffer from that flaw (well, not noticeable to me). And the magnetic mount is great (a magnetic lens cap was dearer than I'd have liked, but worth it for the convenience).