All suggestions welcome.
With two sided VR glass mounts you end with slightly reduced contrast during projection and scanning isn't perfect anymore. Single sided glass mounts are pretty good but film flatness isn't perfect anymore. In all three cases it is a nightmare to get rid off the dust on the extra glass surfaces and there's a risk of fungus over time. Glassless mounts are in general pretty bad but there're no fungus and moisture problems nor an increased dust problem. All in all I am a little bit frustrated with all this mechanical bullshit.