Has anyone used George Lepp's ND filters? Are they neutral in your experience?

I have played with Hitech, got it replaced too but the same magenta (on my E100G slides). I have the round B+W 6 stop and B+W acknowledge it does get a cast due to IR but there is a hot mirror filter available to remedy but the stronger filters don't have this advice online. Yeah .. I am wanting a neutral ND filter square format doing landscapes / cityscapes. I have researched online and the Lee Big stopper appears to be a blue cast. The Hoya appears most neutral but that's round.

It's slide film so gonna be projecting it or on lightbox.