At that ridiculous price definitely get the B+W 10 stop, only 105 bucks!
I stopped using square ND filters a while ago as occasionally I would get reflections on the back of the filter that would ruin the shot.
fair point for some.
However, to be clear where I am coming from. When I'm putting filters in front of $6,000-$9,000 medium format lenses, personally I aim for the highest quality possible, rather than shopping by the price.
To my mind, the best is the SinghRay More-Slow, or the Bigstopper.
The results from either are excellent, with, in MY oppinion, the SinghRay being better.
The 5 stop image quality is also excellent, just the robustness of the filter in the field is horrendous.
So it depends what each person are trying to achieve / use case.