Well I think I read the same stuff as you. I don't remember what was my shutter speed for this video but I think it was a bit too high (like 200 instead of 50). ISO was the lowest possible so that's fine. I have bought the Polarpro filters (but the 3 pack, ND8-16-32) and because I'm in plain bright light, I would have used at least ND 16 to get close to shutter speed 50. That said, I don't really mind for now that my footages lacks the motion blur, it's all test for the moment.
Thank you for your comment