It won't change any minds among the flerfers. Commercial airline flights regularly go to 40,000 feet. You can see the curvature of the earth just fine at 40k feet.
It's clearer at 100k feet, but if you're intent on not seeing it then you still won't see it.
I have doubts that even orbit would change their minds. They've already gone through contortions about why it's night in some places when it's day in others. I am quite certain they're up to the task of explaining why they're over America now and then Africa, previously out of sight, a few minutes later.
It's just not worth arguing with those on intent on being stupid. They can simply say "no" and no power of evidence or logic can force them to do otherwise.
Where is Ocean gate was charged with dealing with pressures above one atmosphere, this company will have to deal with pressures between zero and one atmospheres. Probably the same outcome will occur at some point.
I’m not OP, but the startup ethos of the last few decades has been to move fast and break things, fake it til you make it, and generally operate on the bleeding edge to deliver incredible products (and, occasionally non-credible, cough Theranos).
My concern would be that the team would cut safety corners until the probability of success just barely rises above some threshold, rather than engineering everything to have as low a risk as is feasible. Is 0-1atm easier than 1-infinity atm? Yes, but that just means you can cut more corners.
I buy it. OP's comment struck me as interesting, because the "above 1atm" value turns out to be about 300atm; designing a pressure vessel to sustain a 300atm pressure difference is much more challenging than one to withstand 1atm, which is the case for these balloons. If we assume relative cost cutting due to cultural concerns, then the analogy makes sense.
That said this seems… dangerous. Giving me OceanGate vibes.