It isn't that big of a deal, though I'll try to do some specific testing on that and get back to you. When I'm doing these things, I'm not making any attempt to slow down so, at first, I'll make more mistakes. The only way this is magnified on the TextBlade is that, since your fingers move so much less and there is not as obvious a separation between many, that a change in typing position can more easily cause user error. My particular case may also be magnified by the fact that I'm typing in the exact same position for days and even weeks at a time so I'm not used to making adjustments. I suspect it is much like playing a musical instrument. I can switch from one to another without problem, but I've done that for decades and, since I'm teaching kids on different instruments, these changes are common.
Also, we are talking about some pretty big changes in my case. Right now, in my normal position, my keyboard is on my lap and the way my chair is set up, my elbows are on the armrests (which are pretty low for this reason). My chair is about 15 inches off the floor and the TB itself is about 20.
In the video, the chair height is about 17 inches and the keyboard is about 29 inches. There is NO elbow support and, to get the angle I needed to avoid various issues for making the video (light glare, etc), I was also angled towards the table so each forearm had different support. All affect the feel, especially the second as I actually learned to use that elbow position on the chair as sort of a "home row" for elbows! When in the Apple store, I have to stand up, drastically changing my arm angles and, of course, no elbow support so a big difference to the angle my hands are coming in at until I adjust.
Heck, the feel is also affected by what it is sitting on. My card table in the video allows some cushioning. My lap does too, but it is different. Put it on a really solid surface (granite is great!) and that also changes it. Some for the better, but it is still different at first. Some of these things, if all else was the same, probably wouldn't matter much at all, but otherwise they just add to what I might say is the distraction of things feeling different.
But I'll try to remember to experiment with this by changing my position, but typing as if I need to get things right the first time. To see how many mistakes and how much slower I am at first. But really, it isn't a big deal unless you are trying to quickly create a video of typing speed pretty much at or slightly above your general average right away.