My eyes get really tired/strained looking through a finder for a long time - its more of an "I can't seem to keep one eye shut" issue. My 4x5 doesn't give me that problem, nore does my old TLR with WLF... so I thought if I could find one for my ETRS it might relieve some of that strain. I tend to shoot slowly anyhow, so I don't mind not being able to whip it up to my eye as fast.