Would you say a shopkeeper could pick these up for themself or their salespeople and immediately continue with the same workflow, if they had been using a popular plain calculator up until then?

And it could provide additional layers of local and remote data handling from an easy to administer server app on the owner's phone without the need to concern the end users of the calculators with software whatsoever?

Seems to me one thing the calculator in hand can do is traditional real-time negotiating and discounting. Where something like the distraction of software could be a disadvantge compared to what came before.

The current version looks like a great solution, because it's so basic.

You risk adding too many features (and cost) in the next version.

A cell modem is going to require certification and of course a separate sim-card/data plan. Do they need USB unless they have a computer already? And speakers? Is this to play the radio while tending shop? I'm sure even the most illiterate can still read numbers, so TTS would be just a gimmick IMHO.