Using this last night in a small refractor there was a 'spike' on the sides of brighter stars. I couldn't see anything obvious like a scratch that would be causing it but it didn't happen with other filters. I looked at a streetlight with it and that produced a bigger spike, a bit like what you get from a correct image prism diagonal.
It would be ok for terrestrial use with a small achromat as it does eliminate chromatic aberration but not ideal for astro unless you can live with the spikes.
