Yes, I very much doubt that this will be a vast consumer success like the iPod/Dropbox/etc. (Though since they've already sold through their initial run, it's probably going to be a success for Panic! at least.)
But the meat of the issue isn't related to ultimate success, it's that the famous Slashdot comment, and the grandparent here, aren't getting the point -- they're caught up in a feature list comparison, and missing the holistic element. The iPod was worse than a Nomad in the metrics people were using to compare MP3 players at the time; it was just also a better product.
Of course, telling the difference between a refined product and a pretentious flash in the pan is famously difficult. But that's the theory of why you'd buy the Playdate instead of the Retroid.
(My personal take is that it looks fun, and it wouldn't take many of those first 24 included games being decent to get it to a respectable value.)