Who is a Baha'i?

I read a curious comment the other day - proposing that anyone who accepted Baha'u'llah as a Messenger of God could call themselves a Baha'i. Yet this is not the definition set by Baha'u'llah. He said, not only would a person need to accept His words, but those of his son, 'Abdu'l-Baha and the Universal House of Justice. 'Abdu'l-Baha then stated that to be faithful to Him AND to Baha'u'llah, one had to accept Shoghi Effendi, His grandson as the Guardian AND his instructions. AND 'Abdu'l-Baha specified that succesor Guardians had to be appointed by the Guardian and that appointment had to be approved by the Hands of the Cause.
Some people who claim to be Baha'is are on their third or fourth so-called "Guardian" without following 'Abdu'l-Baha's instructions for determining said Guardian of the Baha'i Faith. So, they have not fulfilled the qualifications for being Baha'i. (and, very curiously, one of those self-proclaimed "Guardians" had earlier signed a statement saying that there was no successor Guardian to Shoghi Effendi. Very curious indeed!!)
It may seem an insignificant matter, but when it is part of the Covenant of God that stretches back to Abraham and Noah - it is more significant.