- is smal, ideally the distance between Braille dots or about (distance within a character is smaller than that between dots in different characters) 2.5 mm by 2.5 mm, with a height of less than 2cm or so,

- can lift a dot by about 1mm (from definitely not above the surface to 0.9mm above it),

- withstands a force of about .3N (30 grams),

- can be switched while the user exerts that 30 gram force on it,

- will work for 10^6 actuations,

- works reliably in the presence of dirt, grease and human sweat,

- doesn't require enormous amounts of power (piezo-electric Braille cells only need power when switching),

- is safe when users (almost) touch them with their bare fingers (piezo-electric cells use 200V or so to switch, but that is at a few cm from the Braille pins),

- can be produced for a few dollars (you need 8 for a Braille cell or 160 for a 20-character display, so it adds up). If your goal is to make a full page (say 8000 pins) $1 each already is too much.

You also wil like want to switch 500 of these in 0.1s or so.

Especially if you forget about the desired reliability and/or limit the force or the travel, the problem gets a lot easier.

I think the videos that these guys posted are real, but wonder how long this device will keep working.