Judging by some comments here and reading the user guide, it may be worth expanding the guide to show the different configurations and the film they hold. There is the one image on page 5 that might be easy to misunderstand. Maybe an insert before the parts list?
This tray holds a single [layer] of film, emulsion side up, for development, correct? So a single 8x10, a pair of 5x7s or 4x10s, or four 4x5s.
I'm in no rush to do 8x10 negatives, but I may have to order one to keep around as a tray for prints. [Would be a good excuse to eventually start doing 8x10 film. That's how logic works, right?]