I've been using a modified Lee SW150 filter holder on my Nikkor 14-24, recently I've been having some issues with the threads jumping when screwing the rings onto my lens. I wasn't happy with the response from Lee, and didn't want to buy another SW150 as there are some serious design flaws with the Lee system, you can read more about that and the changes I made to 'fix' the SW150 in the following post:
I saw an image of the Progrey G150X a while back, and from what I could see it didn't have the same design issues as the Lee holder. The Progrey costs about half as much as the Lee SW150.
Attaching the holder to the lens is easy, place the lens in the large ring, aligning the 4 tabs with the petals on the lens
Place the smaller ring over the lens and screw it onto the large ring.
Slide the holder onto the front ring and tighten the thumb screw.
There are 3 sets of guides included, each has a different amount of filter slots, ranging from 1 to 3.
This image was shot with the sun 90degrees to the right, with a hitech 10 stop IRND and a Lee 0.9 soft grad. The purpose of this shot was to try and force a light leak, as you can see there wasn't one.
This shot was taken under my typical usage conditions for the holder, using 2 x Lee 0.9 ND filters and a Lee 0.9 soft grad. Again there is no light leakage or any other issues. Results are the same as what I'd expect from my modified Lee system.
The only downsides I've found with the Progrey system are:
*It's a lot harder to adapt this holder to take a 4mm polarizing filter, Lee sell 4mm guides for the SW150, but with the Progrey you need to modify the 2mm guides, I modified the two slot guide to take a 4mm and a 2mm filter using custom made acrylic spacers. I switch to these guides when shooting waterfalls. Changing the guides is easy, there's 4 hex bolts holding them on, and its designed in such a way that these can be loosened without falling out of the holder.
Update: I just found out that CaVison has released a 2mm version of the 150mm CPL filter:
That solves a lot of headaches.
*The size of the front mounting ring could be a problem for some camera bags, with the holder removed the ring is a lot bigger than the mounting ring on the SW150.
Advantages of the G150X over the unmodified SW150:
*better design with no light leaks
*Can take 3 filters vs 2 filters for the SW150
*Less weight - I would need to remove the custom baffle from the SW150 to get the exact numbers but the Progrey is lighter
I'd recommend this over the Lee system.