I would take it easy on Sean. I believe he is a good guy and believing Catholic. God save me if I am wrong. Maybe he has some other issues he is dealing with. He's only human like the rest of us.
That being said, I don't hold to any group but judge each chapel or Mass on a case by case basis: 1) Is the priest a valid priest 2) Is he a true Catholic 3) Does he offer the New Mass 4) Does he believe and preach only in accordance with Catholic Dogma and Tradition i.e. not Vatican 2.
If the answers are (yes, yes, no, yes) I have no problem attending be it sede-vacantist, diocesan allowed Latin or Eastern rite, SSPX, CMRI or Resistance.
Sean will lump me together with the sede-vacantists now because I admit it is a valid Catholic opinion, but he has deceived himself in doing so. We are in crisis in the Catholic Church, deep into the crisis. When Sean gets his drum to beat on, man does he beat it. Right now his horse to kick is sedevacantism and he won't let it go. Last year it was whether or not the New Mass gives "good fruit". He went so far as to call up the prior of a well-known Resistance monastery and strike the debate and beat his drum with these priests, of whom I'm sure he gained many prayers.
Indeed, even Bishop Williamson has publicly stated that sedevacantism is a Catholic opinion albeit dangerous in the humble bishop's opinion. So knowing that a great many of Sean's inspirations and motivations are almost certainly motivated on defending the good bishop, he should inquire with him as to whether or not sedevacantists like the CMRI or SSPV are Catholics or schismatic heretics. Then he can beat his drum no more and maybe get back to productivity.