The filter is simply a 3D printed 'X' that slips over the objective lens. I got mine from ThingiVerse, and is very similar to this one:
https://www.thingiverse.com/thing:4608036
The result of about 20 minutes of capturing the Southern Pleiades with the filter in place can be seen here:
https://blog.teamrc17.net/Astro/saywhat/
The spikes are not overly large, and whilst I think they look OK, I don't think I'll be using that filter very much (if at all) in the future.
Cheers,
V