I don't know what it says that my favourites tend to be from the anglophone world despite the breadth of countries covered by the 86 short short stories collected here - personal (culture-shaped) taste, an actually higher overall quality of those ones (perhaps due to either the form being more mature or the best examples being easier to source, not least by all being available in English, possibly via translation), some combination of the two? In fact, although this is almost certainly coincidence, I think my favourite might be the one Australian entry, Josephine Rowe's "The Vending Machine at the End of the World".
The editors deliberately define their scope by feel rather than word length, but in practice the ceiling seems to be around 700 or 800 words, and those that get towards that upper limit feel noticeably longer than the rest. The best do register as a flash of insight or feeling (or both), maybe not exactly out of the corner of the eye, but certainly in motion, and don't rely too much on either the staging of a single symbol, metaphor or image (whether in a more realist/revelatory or Kafka or Borges-type vein), or a final beat, turn or twist that gives the whole thing meaning or shock.
The other stand outs for me: "Please Hold Me The Forgotten Way" by H J Shepard (US), "The Waterfall" by Alberto Chimal (Mexico - the other that might be my favourite, making particularly good use of the short short form), "An Imperial Message" by F Kafka (Czechoslovakia; I've read this one before, and obviously the prohibition on being Kafka-esque doesn't apply to Kafka himself!), "The Baby" by Maria Negroni (Argentina), "Aglaglagl" by Bruce Holland Rogers (US), "Appointment in Samarra" 'as retold by W Somerset Maugham' (England), "The Hawk" by Brian Doyle (US), "That Colour" by Jon McGregor (England).
Reading this made me wonder about the limits of such a short form; the best ones are very good, but I'm not sure whether it's possible to create the same kind of deep effects with so few words that the best 'normal length' short stories can. But: they can probably do something different, which is reason enough.