Clarification due to a somewhat confusing title: This is about the merchant using an iPhone to accept credit cards and other Tap to Pay devices. The customer was able to pay with Tap to Pay with their iPhone for a while now.
I honestly don't see what's so revolutionary about this. Why would anyone shell out multiple hundreds of € when a device that accepts payments can be purchased for a fraction of the iPhone price? E.g the most expensive device here [1] is only 120 €, and it can also print the bill. The cheapest that does the job is a mere 20 €.
Compare that to competitors in the space like Square, which costs ~$300 USD and charges ~2.6% plus a flat 10 cents per transaction.
If you're not doing over $50k in volume per month and already have an iPhone...you might as well just use the Square app and take NFC payments on your phone instead of investing in the reader (assuming you're operating in a space where consumers will readily have NFC payments ready).