Answer from the manufacturer:
Thank you for this very interesting question. Indeed, part from the firmware version, there is no difference between the Wireless Pulse Oximeter (PO3) and the iHealth Air Smart Pulse Oximeter (PO3M). The M has only been added for "medical".
Thank you in advance for your understanding.
I guess the Google translator hit it out of the park on that one.
I have now ordered the available non-Air and received the newer Air. Maybe it's just the pictures that are not up to date.