I haven't seen a lot of information on these reels, and only occasional references to them, so I thought I'd post a mini-review after using one for the first time.

Site: https://20thcenturycamera.com/collections/film-reels

The reels are partially 3D printed, and partially industrial plastic. The ends are sturdy, the arms are flexible, and probably won't stand up to abuse-- but neither will the film you're loading, so that's probably not an issue.

The ends of the reel have flat edges-- at least for the 4x5 reel, this makes it easy to lay the reel on it's side, and slide the film (emulsion down) into the easy to find slots.

Once the film is in the slot, you can press on the edge of the film to slide it into place. To retain the film, the slots end in a V notch, and the opposite edge of the film is held in place by the slightly springy arm, which has a hook on the end. This also forces the film into a slight curve that keeps the emulsion surface from touching the plastic. To remove the film, press lightly on the edge of the negative until the hook lets go, and the negative will "pop" out a bit as it straightens, making it easy to remove.

This is as opposed to the mod-54 design where you "taco" the sheet into notches on each arm-- my complaint with this design is it looks too easy to get the wrong notch in the dark. If there's a way to screw something up, I will find it, so I try to avoid such designs.

After a few practice loads in the light, and then with eyes closed, it was easy to load in the dark.

The reel fits nicely in the Paterson System 4 tank, and was easy to develop with-- although the requirement for 1L of chemical is... painful, unless your chemicals are plentiful and cheap. It takes 950ml to fully submerge the reel in the tank.

The SP-445 is more efficient (half the chemicals for 2/3's the film), but the biggest advantage for me, is it holds one grafmatic worth of film.

The other nice thing is that since it's 3D printed, it's very easy for 20th Century Camera to offer other sizes-- anything from 2.25x3.25 up to 8x10, including 9x12.

All in all, I'm pleased with it, and will definitely use it again.