Earlier quoted context omitted.
Like the feedback of smartphones? Especially those prior to the very recent vibrate on touch People want to type, and they want to do it quickly. Tactile feedback is nice... but most people do not engage in typing for the fun of it. The primary concerns for this are input reliability, ease & speed of setup, and learning curve. You aren't using such a thing to replace your desktop keyboard. You're using it to replace…
Smartphones work to some extent because they are relatively light and you hold them in your hand. This means it is very much not a rigid surface. Typing on a projective keyboard on e.g. a desk is very unpleasant, because you are pecking a hard, rigid surface with your fingers.
I can't trust emails on a smartphones because they're so error-prone. If this thing is reliable in its input, and easy to setup, then the "unpleasantness" of typing on a desk is very low on the list of concerns, unless it's extremely unpleasant, if not outright painful.
And unless you're a hunt-and-pecker (which couldn't feasibly use the tool in the first place, afaict), I don't see how it could be that unpleasant. And playing with the idea on my desk.. it's not the greatest feeling, but its hardly a showstopper.
It's not a general keyboard replacement. It's a few-usecase and higher-constraint keyboard replacement; the only thing that matters is whether it supports those specific fewer usecases significantly better than the currently available alternatives, because it doesn't hinder using the general tool as a fallback.