The price for both is similar to others on the market. The two popular brands in the UK - Lee Filters: £100 and Formatt Hitech: £130 compared to 84.5: £95 so you're not going to save heeps of cash with this filter but certainly going to help, especially when it compares to Formatt Hitech or Nisi where they are priced around £130-150 a filter.
Why you should consider the 84.5 X-Stopper? Firstly its made of mineral glass and the first worries would be its more prone to crack or get damaged because of this. Yes but its very strong, that said I wouldn't want to drop it from table height unlike the rest of the range 84.5 filters in which I recently tried out and the graduated filters took some knocks and this wasn't an issue. This heavier glass filter I feel more protective off and it even comes in its own protective sleeve for on the go.
The X-Stopper also has a foam gasket glued to the filter to help reduce lightleaks. It would had been nice to have the option to have this fitted or to do myself but personally I'm happy they did or I may have messed this up myself.
With the X-Stopper and foam gasket plus Formatt Hitech Firecrest holder set up its virtually lightleak proof! But the filter is very snug in the holder and extra care has to be taken to fit the filter in and taking the filter out which is slow but considering what the filter is used for. Slow is nothing to worry about.
The X-Stopper has had no colour distortion and setting a custom or even just leaving the camera on auto white balance has worked perfectly in good light and low light and has worked in a range of filter holders although be it, stiff and somewhat slow to fit.
As a whole I've thorough enjoyed the 84.5 filter range and will continue to use them going forward.
Below is a collection of images using the X-Stopper. The river photographs have had no colour balance altered in post. Some of the ICM photos have been altered for artistic effect.
Otherall, very impressed with the X-Stopper and as a whole I would consider this ND as a serious option if you're interested in long exposure photography. With no distortion, colour casting and a partially less expensive option its a winner all round. It even comes in its own little protective pouch.