There should however not be any differences besides a card being more convenient
That is indeed the case, I asked in the office when I got mine about it being rejected because there is no photographic evidence on it. They gave me a small sheet of paper I can bring along with it explaining that it is a legal document and it must be accepted as such. I have never had a problem with it being accepted, but I always carry the legal sheet with the Karta Ponytu just in case.
But yes, a photo card would be much more convenient.