Marumi's amazing Magnetic Graduated Neutral Density use science, rather than slots ...
If you forget the set the white balance on your camera, photo-editing software can easily fix that. But what do you do when your image has mixed lighting? Combined, Lightroom's local adjustment brush ...
Cokin's Z-Pro Nuances Extreme Graduated ND filters are some of the most expensive on the market, but I reckon they're worth the asking price ...