Now that I have a printer that can print flexible filaments again, I've been able to try out a few TPU cases for my Librem 5 (I modified a Librem 5 slim model to remove most of the back). I tried printing face up and face down with supports to see what worked best for my printer.
I think I'm leaning toward the red case, although I do have some old black Ninjaflex I might try out later.