As much as i love shooting with the smaller mirrorless cameras (Sony A7R3 + GH5s) as they are much easier to pack up and handle all day, I really despise the lack of having built in ND Filters. Having to thread filters on and off slows down the process of filming.
So what I ended up doing was permanently adding these Swing Away Filter Holders to my most popular run-n-gun lenses. When I need the ND Filter, I leave it down, and when I don't need it, I swing it away. I've also added lens caps over the nd filters so I never have to remove the adapter.
I could have just purchased one or two filter holders and shared them between lenses, but I decided to spend the extra money and just have one for each of my most widely used lenses. Over the last 9 weeks i've been using these adapters, I feel like it has made our productions so much more efficient. Quality of build is excellent, and I suggest everyone have at least one of these in your kits.
The only advice I have if you plan to use these ND Filter adapters on your lenses, is to make sure you use filter step up rings, and choose oversized ND or CPL filters. These swing away filter holders protrude a bit from the front of your lenses, and you may end up seeing vignetting, so you should go with a bigger size. If you're lens filter thread is 58mm, use a step up ring and purchase a 67mm holder, and finally add a 77mm ND Filter to the end.If you're lens is 72mm, try to step it up to an 82mm, etc. etc.