Lee is great, but perpetually out of stock - you have to get lucky and act fast.
For screw in 10-stop, I use an 82mm Schneider Optics (B+W's parent company), and a 77mm B+W. both are very good, but have a slight warming tone.
Haven't heard of the brand you mention, but putting a cheap filter in front of a good lens isn't optimal.
Stay away from variable NDs - good ones are ok for normal/tele lenses and often moderate wide angles. But a variND is basically a pair of stacked polarizers, and with an ultrawide lens, the uneven polarization you see with a CPL in the sky manifests as a 'Maltese cross' artifact (affecting all shots, not just sky).