In practice, it makes no difference to the card holder, because Curve currently treats consumer and commercial card holders the same. As commercial cards are exempt from the ban on merchant surcharges under Article 62(4) of Directive (EU) 2015/2366, it is possible that merchants might refuse or surcharge commercial cards, but in my four years of using Curve, I have never experienced this. This is more common with credit cards than debit cards, and of course Curve is the latter. Even HMRC, which surcharges commercial credit cards, does not surcharge commercial debit cards, as it unsurprisingly does not want to create such a barrier to businesses paying their tax.
But for Curve, commercial cards make a massive difference. Commercial cards are exempt from Regulation (EU) 2015/751, which caps interchange fees at 0.2% for debit cards and 0.3% for credit cards, so Curve receives much higher revenue from merchants with interchange fees uncapped at around 1.25% to 1.65%. This means that Curve can use this additional revenue to fund the capped 0.3% interchange fee that it pays when you use debit-fronted credit, but nevertheless Curve unnecessarily charges its new 1.5% non-metal fee on commercial cards.
As a genuine commercial user (at least partially), I prefer to use a commercial card as I believe in the product and want to boost Curve’s revenue via the much higher interchange fees. When a merchant stubbornly doesn’t accept American Express and I have to use Curve instead, it gives me pleasure to know that the stubborn merchant is paying more to accept my commercial Curve card than if it accepted Amex, and that this additional cost benefits Curve.