Nice one, I was edging that way anyway so I think that's what I will do. Which is the better one to invest in?
Dangerous question
Both LEE and Nisi give fantastic images. Nisi are a smidge more expensive mainly because they're made from glass instead of resin (however, the ND filters, small, big and bigger stopper from LEE are made from glass as well)
Personally, I think you can't go wrong with either. When you look at videos comparing them, the way you add a circular polariser on the Nisi system seems much bettrt, and with quality it seems like the Nisi filters do take the edge, but I believe you have to REALLY pixel peep to find the difference. One YouTuber reported up to 20% difference, but I have NO idea how he measured that.
I went with Nisi simply because I fancied it and taking a "balls to it" approach - I am sure I would have been just as satisfied with LEE if I had gone that route. Although I have to say the presentation from Nisi when unpackaging a filter is awesome.
Oh, and on the LEE big stopper as mentioned before, it is often reported to give a blue colour cast. Easily fixable in LR, but it's an extra step you have to take.
Also, as finally, I went for the LEE filter holder which holds Nisi's just fine. And the LEE filter pouch is great as well