I too liked the review and it has tempted me to consider purchasing the Kood filters. However, the article was about graduated Neutral Density filters, whereas everything I read about the Kood GG filters seems to suggest that they are graduated grey filters, not neutral density filters. Does this make a big difference?
Indeed, Kood do make Graduated Grey filters as opposed to Neutral Density! They work in much the same way as ND filters but they aren't truly neutral in tone; you may find that they have a slight blue-green colour cast to them.
You'll still get amazing results out of them but you may want to just slightly adjust the tones during post-processing. This is one of the reasons they're so cheap!