Hi @atmospheric-haze, thank you for enjoying the images, no I don't recommend getting variable NDs, you'll end having awfull vignette and uneven effects, the best solid ND filters are the square ones that you slide into the filter holder or screw-in ones but the problem is you will have to screw and unscrew them every time you want to change it, it's easier to just slide them in and out of the filter holder. The ND graduated ones are the rectangular ones (100mm x 150mm) that you also slide into filter holder, this way you can always adjust the position of the filter regardless your composition, I would also recommend buying good quality ones (Progrey USA, LEE, Formatt Hitech or NiSi) - better to get couple of good ones than a set of poor quality ones that will ruin your shots by adding weird colours to the sky, hope this helps a bit...