The real danger is the INDULT mass! The real danger, is attending a TLM at your local parish, because then you are sucked into the Roman vortex and become neutralized...no more condeming V2, no more criticizing the pope, just go along and be quiet. That solves nothing, and it's exactly what Rome wants.
There are different reasons underlying why people do what they do, one has to understand these root reasons to understand why people do what they do.
I'll just give my root reason why I only attend the SSPX masses:
1) I have serious doubts about the Conciliar church consecrations of bishops and ordinations of priests.
2) I am not and never have been an SSPX "groupie" because they teach their seminarians that some Moslems, Bhuddists, Hindus, Protestants, Eastern Orthodox...... any non-Catholic can be saved. I consider that teaching the root cause of the Vatican II revolution.
What these roots produce is a person who is strictly seeking an undoubtably valid priest that can administer the sacraments, and
that is all I can expect. I don't expect much more. I have no effect on anyone but those around me, so, I can't "affect Rome" in any way and "Rome" can't affect me. As lay people, we are all already "neutralized" and always have been.
If I am traveling tomorrow, and the only available mass choices are a sedevacantes mass by a non-SSPX ordained priest (I have doubts about the the validity of sedevacantes priests who were not ordained by the SSPX) and an Indult mass with a priest that I know was ordained pre-1968 or who was ordained by the SSPX, I will go with the Indult every time.
If I have a choice between a "Feeneyite" priest who is ordained in the new rite and a sedevacantes SSPX ordained priest who preaches salvation for Moslems...., I will go with the sedevacantes.