When I got the Nikkor 14-24 I also got the Lee SW150 filter system, at the time there weren't many other options for using filters on the 14-24.
I've had a Progrey Aurora 0.9 soft grad and 0.9 reverse grad for a while now, I finally got a chance to compare them to the Lee filters.
I rarely use my Lee hard grads, my go to filter for seascapes and landscapes is the Lee 0.9 soft. I owned a Singh Ray reverse grad when I had my D7000 & Nikkor 10-24, but rarely used it as the reverse graduation didn't start early enough so it was basically a 1.2 grad (probably would have worked better on a full frame camera) and it had a strong color cast.
Comparing the Lee and Progrey 0.9 soft grads, the Progrey has a slightly softer transition than the Lee. Color balance looks slightly different when holding them side by side, the lee has a slight purplish tinge when held next to the progrey. I always play around with WB in post so a slight cast either way isn't an issue for me. Straight out of the camera the Progrey looks slightly more natural to my eye, there's not much in it though.
The comparison images are all straight out of camera, shot with the D810 and 14-24. All are at 14mm unless stated otherwise. There might be some variance in the positioning of the filters in some of the shots, I was trying to go as fast as I could to avoid changes in the lighting conditions.
The above image set is a good example of why I prefer soft grads, if you look at the reflection in the water on the left and middle images it is slightly darker than the sky, the exposure looks balanced right across the frame. The reverse grad must have its hard edge positioned right on the horizon, resulting in the sky being darker than the reflection in the water, this is easily fixed in post but if I use a soft edge filter it's something I don't have to worry about later. The reverse grad does give a much more even exposure on the sky than the other two.
When the image is composed with a bit less sky in the frame the reverse grad acts more like a normal grad as the reverse graduation doesn't start within the frame, it also appears slightly stronger than 0.9 as the darker band covers the sky.
Again you can see the difference between the soft and hard edges, balance looks better in the left and middle images. The image on the right will need more work to reduce exposure on the landscape in the middle 1/3rd of the frame.
Keep in mind I'm shooting all these at 14mm on an FX camera, if you shoot longer focal lengths (or use a camera with a smaller sensor) the soft edge grads will be too soft, you'll be better off with the hard edge filters.
I really like the what the reverse grad does for the sky in the images like these, I find most of my images are in landscape orientation with the horizon above the mid point of the image, so I won't see all the benefits of the reverse grad. If I could buy a reverse grad with a softer bottom edge and a slightly thinner dark band I would buy it in a heartbeat, and rarely use any other filter.
Which brand would I choose? The performance is close enough that I would use whatever one I pulled out of my filter pouch first. The Lee seems have a slight color cast when compared to the Progrey but all the time I've been using the Lees I haven't noticed it until now. If I was buying a new set of filters, the Progrey filters have a big price advantage over the Lee filters (using Progrey USA and BH Photo for pricing) that makes the decision very easy for me.
Progrey G100X Filter Holder
I also received a G100X to review but I do not have any compatible filters so I cannot provide any sample images. I did own a Lee 100mm system but sold it a few years back.
Overall design is similar to the G150X holder, but this one mounts to the lens using the filter thread.
There is a thread on the front of the mounting ring to attach a screw in CPL, the biggest CPL I have is 77mm, the thread is larger than that, I'm thinking 82mm but don't take my word for it. There are two openings at the back of the ring so the CPL can be rotated with grad/nd filters in place.
Once the CPL position is set there are two 'sliding doors' that seal the backside of the holder to prevent any light leakage.
The holder is fitted with 2 slot guide rails in standard form, there are also a set of single slot rails and a set of 3 slot rails included. There are some rubber gaskets that can be attached to the front side of the holder for a better seal against the filter.
Both parts of the holder come with their own pouches, although the whole lot will fit in the larger pouch.
Disclaimer: I was not paid for this review nor was it influenced in any way. Progrey USA provided me with review samples of the 2 Progrey filters and the G100x holder for the purpose of this review.