If you read my post again you'll notice that B&W filters were included in comparison with very good results. However, in general
all ND filters, particularly darker than 1.5 will introduce some troubling coloration, even the best brands. Luckily there's rarely any need to use such dark filtering. B&W ND8 MRC filter performed nicely with pleasant, slightly cooling effect which is much more appealing than notorious magenta tint of cheaper brands. The only minor drawback was the weight of tested B&W filters, significant due to brass housings, which may cause the gimbal to work harder or require some custom balancing. Later I've discovered Formatt Hitech brand and purchased a set of 3 filters (0.6, 0.9 and 1.5 density). Nicely made, perfectly weighted and fairly neutral. With exception of 1.5 density filter, which introduces some coloration into video as expected. I'm using mostly FH 0.9 in average sunny summer day with good results.
39mm-67mm Circular Firecrest ND Filters (SuperSlim Stackable)