Slide Cube vs. Carousel

Slide Cube Advantages

• Slides can be stored in slide cubes with much greater density; you can store about five times as many slides in a given volume. I have a fire safe that I store most of my slides in. On a small fraction of them would fit if they were in carousels.
• It's much easier to edit a slide cube - if you want to pull or add a slide, you don't have to tediously shuffle all the others.
• Slide cube projectors have a preview window where you can see the next slide that will be projected, which I find quite handy (I can think about what comment I will make on the next slide while the current slide is being viewed). You can also use the preview window to scan through all the slides in a cube without having to set up a projection screen.
• You can drop a box of slides in a cube and immediately project them, editing as you go; the preview window has an eject button so you can pop a slide out and reorient it if necessary.
• Back in the days when slide cube projectors were made, storing slides in slide cubes was much cheaper than storing them in carousels.

Slide Cube Disadvantages

• Slide cube projectors jam easily. You can't just hand over the controls to someone and leave the scene, because the operator has to know how to unjam the projector if necessary.
• You can only go back one slide, while a carousel projector lets you go back as many as you want.
• You can't leave a slide cube projector on autorepeat, because the slides have to be pushed back up into the cube after being projected (and anyway, it would be sure to jam eventually!)
• If you have a long slide show, you have to swap carriers about three times as often (a cube holds 36 to 43 slides, depending on mount thickness).
• You can't buy new slide cube projectors, and new cubes are hard to find. They are still made, but now cost about as much per slide as carousels do. You can find both projectors and cubes on ebay, though.
• Slide cubes are more fragile than carousels. The covers are held on by thin plastic tracks engaging tiny plastic pins. I've broken a few over the years.

Tossups

• Slide cube projectors and carousel projectors each have advantages when you're trying to “seek” to a particular slide. If you know the number of a slide, many (most?) carousel projectors will let you go directly to that slide without having to go through all the others, and will then let you skip the rest of the slides so you can remove the carousel. A slide cube projector requires that you scan through all the intervening slides, and similarly scan through the rest before removing the cube. It can do this rapidly and without any of the skipped slides being projected (the lamp shutter remains closed while you are scanning), but it does take time. For that matter, slides in cubes do not have numbers anyway.
  The slide cube projector has an advantage if you don't know the slide number. While you are scanning, each slide appears in the preview window before going on to the projection slot, so you can stop the projector when you see the one you want to show. If using a carousel projector, you would have to project each slide in turn to determine if it's the one you want to show.