We're talking about train station displays, not arbitrary displays. Nobody has ever done word processing on a split-flap display so obviously I'm talking about a restricted domain. They don't need to display arbitrary information and the range of information they need to display rarely changes since that typically involves construction. The noise, an unintentional consequence of the mechanism, provides utility to train travelers and is therefore a feature.

In a busy train station the duration of the split-flap change provides an auditory clue to what's going on. If you hear one or two rows update then nothing out of the ordinary is happening. If you hear several rows update that might be a good indication that your train is now on the board, or it could signal mass delays. For many years I went through 30th Street Station in Philadelphia with a split-flap board in the middle and I loved that board. When I'm at airports with LCD boards, I always miss it. LCD boards are trash, you don't notice them changing unless you're staring at them, almost always have text too small to read unless you're standing directly in front of it, and are completely soulless.

I learned to type on a Selectric years before my family bought our first computer. I haven't touched one since.