Not completely worthless. It is possible to convert them to hold glass plates.
Particularly if you have a pack of the film as it contains a spacer to provide the proper depth..
Actually, I think that it's a neat way of doing wetplate with a speed (or other camera) in theory.
I haven't tried mine out yet as I lack the funds for wet or dry plate but would love to try it.
It's a shame that pack film isn't available anymore, i've used a few packs and it is the greatest thing there is... Seriously the most convenient stuff.. so fast and easy to use. It's a shame.. Screw grafmatics and readyloads.. Give me a stack of pack films...