I think you may have misinterpreted @pngwen's post. I think he/she was making a joke saying a casual user can't use a device that they can't touch and hold. I'm not sure I understand what you mean by "how the physical keys feel." Nobody who has pressed a key on my TextBlade has commented on it feeling strange. The most common reaction is that the key feel is more normal than they expected based on its looks.
I think the answer to the question of whether or not the TextBlade is an appropriate keyboard for the casual user depends somewhat on what the user plans to do with it. If they plan to use it with their phone/tablet to replace the on-screen keyboard, my experience suggests that those users would not be impacted by what you claim is "too unusual in the way certain keystrokes are accessed."
I think that all of the talk about key combinations and custom mappings that you see on this forum is associated with users that are wanting to use the TextBlade for all of their keyboarding needs and who are heavy users of keyboard shortcuts.
I haven't seen any discussion here that suggests that anyone would find an on-screen keyboard preferable to the TextBlade. The only concern I see is for the casual user who expects to touch-type without spending any time acclimating to the device. This took a little while for me. It didn't take any time for my teenage daughter.
Speaking in sweeping generalizations, I expect that the toughest transition would be for elderly touch-typists whose fingers have been trained with many, many years of practice to reach a further distance than the TextBlade requires. I also expect that these are the same users who would have the most difficulty adjusting to on-screen keyboards or cramped portable Bluetooth keyboard alternatives. As a result, even these users may find the TextBlade to be the best alternative for them.